1. A 41-year-old CKD 5 female received a deceased kidney offer, 000 mismatch. There is no DSA. The donor was 34-year-old, died in a road traffic accident. No past medical history with excellent kidney function. There was no blood sample or lymphoid tissues available to run the crossmatch.
What information do you need to know to support your decision?
Will you accept this offer and go ahead with the transplantation?
What is meant by virtual crossmatch? What are the pros and cons?
292 Comments
Alyaa Ali Mohammed
Other informations needed
Blood grouping, virology screening ( HCV, HBV,EBV,CMV,HIV)
History of sensitization by Blood transfusion, pregnancy
HLA typing by luminex
Yes I will accept and proceed for transplantation
Virtual crossmatch is a technique to assess immunologic compatibility between recipient and potential donor by analyzing the results of their HLA typing and the recipient-owned anti-HLA antibody without using the donor lymphocytes
Pros
Virtual crossmatch shortens the cold ischaemia time and reduced delayed graft function, useful in cadaveric donors , shorten wait time and improve outcomes for sensitized patients.
Cons
Serum results must be within 3 to 6 months as antibodies vary with time
False positive results in presence of low title or non complement binding antibodies
False negative as it can’t detect null HLA alleles
1-
We have to if the recipient is sensitized
Previous blood transfusions, pregnancy, abortions, SOT…
2
DSA negative
Crossmach negative
==>
We can accept this donor and go forward transplantation
3- The term “virtual” crossmatch refers to a process in which the clinician or laboratorian uses the results of two actual laboratory tests (the anti-HLA screening results and the HLA type of the donor) to deduce what the result of an actual crossmatch might be, should one be performed.
Strengths
○Fast test
○Important in case of sensitized patients
Weaknesses ●false-negative result if there are not enough antibodies binding to the RBCs to cause a reaction
●uncapable to identify null alleles
●may identify non-complement binding antibodies so this results of the increasing of excluded donors
What information do you need to know to support your decision?
Blood grouping of both donor and recipient,Infection screening including HIV,HBsAG,HCV ,any prior history of TB in donor,Detailed HLA typing of Both Donor and recipient,Luminex test of the recipient ,not later than 3 months reports should be available,H/0 sensitazation of recipient like blood transfusion,prior transplant,pregnancy H/o etc.
Will you accept this offer and go ahead with the transplantation?
yes donor should be accepted , No mismatch at HLA level and DSA negative .
What is meant by virtual crossmatch? What are the pros and cons?
Since the introduction of Luminex-SAB it is now possible to ‘virtually’ compare specifc anti-HLA antibodies in the recipient with the HLA profle of the donor. Tis is known as the virtual crossmatch. Te correlation of the virtual crossmatch with fow cytometry crossmatch is greater than 85%. It requires HLA typing of the donor and a recent anti-HLA profle of the potential recipient. To ensure a correct anti-HLA profle at the time of the transplant call, regular collection of sera every 3months is required for antibody screening via solid-phase assays, because antibody titres and specifcities can change over time.
A false negative virtual crossmatch can arise for a number of reasons. Incomplete typing of the donor, as well as donorspecifc antibodies in the recipient serum against a unique HLA epitope which is not available on the SAB panel, can give rise to a false negative result False positives may also occur, as mentioned previously, as a result of antibodies directed at HLA epitopes that come about secondary to denatured HLA antigens on the SAB . Yet another cause for a false positive virtual crossmatch is the presence of null alleles, which are not expressed as antigens on the cell surface in vivo .
One of the principal advantages of performing a virtual crossmatch is the detection of acceptable and unacceptable antigens . Tis avoids unnecessary shipping of organs resulting in less surgery delays, reduces cold ischaemia time, encourages cost savings and improved odds of transplanting highly sensitized patients.
This donor can be accepted being of young age, no significant medical history offered, absence of mismatch and DSA.
Information needed to be recognized is blood group, HLA typing , serology as HBV,HCV,HIV, CMV, EBV, and Toxoplasma , history of blood transfusion ,history of pregnancy and abortions, history of alcoholism.
Yes, I will accept this offer. Based on the mentioned information previously.
Virtual crossmatch is best explained by the prediction of presence of antibodies in the recipient serum to the proposed donor HLA thereby detecting the probability of rejection.
For more accurate results CDC and flow cytometry crossmatch by luminex can be performed. They provide better classification and determination of sensitization states of the recipient, consequently direct to the need for desensitization or not according to the MFI levels of donor specific antigens prior to transplantation process as well as the use of the suitable induction therapeutic agent.
The advantages are being cheap, fast, available, can be done even after donor’s death. While the drawback is mainly being less accurate so it is less reliable.
This donor can be accepted after doing virtual crossmatch using the data of HLA report.
History of blood transfusion and previous sensitization to the recipient is required beside full clinical history of the donor.
Virtual crossmatch is the process of assessing the result of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch.
41-year-old CKD 5 female
Received a deceased kidney offer
000 mismatch
No DSA.
The donor was 34-year-old, died in a road traffic accident. No past medical history with excellent kidney function.
There was no blood sample or lymphoid tissues available to run the crossmatch.
● What information do you need to know to support your decision?
Blood group
History of pregnancies and abortions
History of Blood transfusion or transplantation
Donor HLA typing
● Will you accept this offer and go ahead with the transplantation?
With negative cross match and DSA I will accept this donor
● What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests : patient anti-HLA antibody and donor HLA typing.
● Pros :
☆ It is useful in cadaveric transplantation work up.
☆ Shorter wait time
☆ Improved outcomes for sensitised transplant recipients.
☆ Permits transplant physicians to consider donor organs that would not otherwise be available by means of a prospective crossmatch strategy.
● Cons :
☆ A VXM does not identify ‘null alleles’
☆ False positive results of may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors
☆ It can give false negative results due to the fact that the list of all potential HLA donor antigens have been classed differently
What information do you need to know to support your decision?
ABO blood grouping, HLA typing, Latest Luminex test for DSA in donor blood best, Virology screen HBV, HCV, HIV, CMV, EPV, Detailed history of malignancy.
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept the offer and go ahead with the transplantation
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch is a risk assessment tool used to ascertain the presence of HLA antibodies in the recipient’s serum and to determine the potential crossmatch results with an available donor virtually. Recipient sensitization towards different HLA can be predicted before performing actual CDC and Flow cytometry crossmatch. For a virtual crossmatch, we first analyse and titrate the levels of anti-HLA antibody in the recipient’s serum by means of Luminex platform. The level of these antibody is measured in terms of Mean Fluorescence Intensity (MFI). MFI >1000-2000 is considered highly significant which has the potential to convert a CDC/ Flow cytometry crossmatch positive. These antibody levels are then directly corelated to donor’s HLA antigen profile and a virtual crossmatch is established.
Pros: 1. Used in case of both the sensitized and non-sensitized patients
2. Predicts actual flow cytometry cross match results, facilitating rapid allocation of organs in highly sensitized recipients.
3. Some studies have shown the statistically significant reduction in cold ischemia time with the use of virtual crossmatch.
4. Virtual cross match is possible both at the time of organ allocation and after organ allocation. Cons:
Less reliable compared to another crossmatch testing available
Reference
1. Clifford Sullivan H, Krummey SM, Gebel HM, et al. Physical crossmatching vs virtual crossmatching: the end of an era? or why give up a good thing?. Hum Immunol. 2020;81:401-406.
2. Rao, Prakash; Deo, Dayanand; Marchioni, Misty; Harris, Patricia. 117.4: The virtual crossmatch: A useful tool to improve organ allocation. Transplantation 103(11S):pS12. 2019.
Q1: We need the BG of both the recipient and donor for ABO compatibility and their HLA typing. In addition, a recent Luminex test of the recipient and the history of sensitizing events like pregnancy or transfusion screening for viral infections and its history are necessary. Q2: Yes, they are zero mismatches, no DSA and if the result of VXM is negative and ABO compatible, they are a suitable donor. Q3: virtual cross-match is not a physical cross match but by using donor HLA and antibody screening of recipient by Luminex, one could determine the result of cross-match. For virtual crossmatch at least one recent result less than 3-6 months should be considered. False positive: low-titer or non-complement binding antibodies results in the wrong exclusion of potential donors. False negative: due to misclassification of HLA Ags. virtual crossmatch does not include null alleles of HLA. Null HLA alleles are determined by molecular typing but do not express them on the cell surface. When a null allele in the recipient is considered fully expressed, especially in HSCT, there is the risk of developing DSA which can affect future transplantation. Advantages of VXM: shorter cold ischemic time in deceased donors. Disadvantages of VXM: false positive and false negative results as mentioned earlier
1. Choose the correct answer regarding Null HLA alleles A. It could be missed on VXM B. It is unexpressed HLA but identified by molecular testing C. More important in renal transplantation D. DSA against unidentified null alleles can cause an immunological challenge E. All the above
VXM can not identify null allel as expression of allel is not checked in VXM A true
B is true as THIS STATEMENT is the definition of null allel
C need some explanation from proff
D why DSA will develop if null alllel is not expressed ?
• What information do you need to know to support your decision?
In Deceased donor transplantation
The following should be checked including
1. ABO blood grouping
2. HLA typing
3. DSA in donor blood best technique is by luminex recent one
4. Virology screen HBV, HCV, HIV, CMV, EPV
5. Proper history and history of cancers
6. History of active or old infections
• Will you accept this offer and go ahead with the transplantation?
First i need to check for ABO compatability
This Deceased donor is 000 mismatch with no DSA even in absent cross match
I shall accept this Transplant
What is meant by virtual crossmatch? What are the pros and cons?
It is a virtual or not physical cross HLA cross match between donor and recipients to detect possible antibodies in recipients blood
Regarding Pros : rapid test offer a good prediction of the prognosis of the tx even before true cross match
Shorten cold ischemia time
Regarding Cons
1. Not a quite reliable test especially if done more than e months
2. False positive in case of non complement binding antibodies or low titres of Anti HLA antibodies
3. False negative especially in null alleles where there is no expression of HLA on cell surface
Q1- What information do you need to know to support your decision?
I need to know
A- Blood group compatibility.
B- Sensitization state ( PRA% , HLA typing , any previous crossmatch, history of previous transplantation, blood transfusion, revious pregnancy)
C- Underlying cause of renal failure .
D- Renal biopsy if present .
E- Virology screen hepatitis B,C. HIV, CMV , EBV, herpes SIMPLEX .
F- Malignancy history .
G- We can do virtuall crossmatch if blood sample is not available .
Q2- Will you accept this offer and go ahead with the transplantation?
Yes, I do accept this offer as the as there is 000 missmatch, no DSA , and young age donor And no obvious contra indication .
Q3- What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatching
In virtual crossmatch (VXM), both donor HLA typing and solid phase antibody screening are utilised together. It is not real a crossmatch of mixing serum and lymphocytes. The data is used to forecast the actual in vitro crossmatch results by “mixing” identified antibody specificities of recipient serum with donor HLA antigens .
1- The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
2- VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a prospective crossmatch strategy, and thereby, allows to consider a potentially positive crossmatch a risk factor for donor selection .
3- Titres, specificities, and presence or absence of antibodies could significantly vary over time. Thus, the use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty. The VXM should, therefore, be done considering all available serum results including at least one recent within less than 3-6 mo for a given patient.
4- False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors .
5- The VXM can also give false negative results due to the fact that the list of all potential HLA donor antigens have been classed differently and, therefore, can not be correctly represented .
6- The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
7- VX-M does not identify the HLA “Null” alleles.
Reference:
Aslam S., Buggs J., Wyatt K., et al. The impact of virtual crossmatch on cold ischemic times and outcomes following kidney transplantation. Ann M Surg. 2021;87:109–113. doi: 10.1177/0003134820942180. [PubMed] [CrossRef] [Google Scholar]
⭐ ⭐ in the present scenario, no blood sample to perform wet cross match…so we can depend on Virtual cross match or not ….it depends on:
_History of recent sensitization as blood transfusion , infection or even vaccination that can produce newly formed DSA which necessitates wet cross match to confirm that we can proceed to transplantation.
_ Also , we need to know the blood groups of both the donor and recipient.
⭐ ⭐ based on that 000 mismatch and negative DSA, that means that negative VXM (depending on HLA typing of the donor and DSA detection in the recipient by luminex single antigen bead).
We can proceed to transplantation if no recent hx of sensitizing event..
_If postive hx …that means false negative VXM and postive DSA (which will have postive FCXM).
_Null HLA antigens are HLA molecules, not expressed on cell surface and detected only by microscopic or high molecular diagnosis.
_It can induce DSA, and have immunological consequences especially in HSCT more than SOT.
⭐⭐pros:
_virtual cross match is rapid, decrease cold ischemia time in deceased donor and nor require essential transfer of samples across long distance.
⭐ Cons:
_give false negative results is recent sensitizing event, do DSA should be repeated every 3 months while on the waiting list or essentially requiring wet cross match.
The important information required is:
Blood group of donor
Any co-morbidity such as diabetes, hypertension, CVD
Viral profile such as Hepatitis B, C, HIV, CMV
Past history of malignancy Would you accept this offer?
Yes Virtual cross match Virtual Crossmatch is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch. Pros: Shorter time to transplantation Cons: Less reliable compared to other crossmatch testing available
1- We need to know the Blood group to check ABO compatibility, as well as tissue typing and viral serology.
2- since this is a deceased donor offered, probably ABO compatible (directly transplantable ?)
3- As the name explains, it is not a physical crossmatch. Rather, it compares the antibodies present in the recipient against the HLA of the potential donor.
What information do you need to know to support your diagnosis:
We need information about,
1. HLA typing,
2. Blood grouping,
3. Virtual cross match report,
4. Viral serology report,
5. The cause of renal failure in recipient,
6. Previous transplantation,
7. DSA level.
Will you accept this offer and go ahead with the renal transplantation:
I will accept this donation as there is no such high risk and contraindication.
What is meant by virtual cross-match and what are pros and cons:
The virtual cross-match is the process of assessing the result of solid phase and cell based HLA antibody identification assays to predict the result of physical cross-match.
In contrast to physical cross-match, the virtual cross-match does not need viable donor cells but relies on complete HLA typing of the donor and current antibody assessment of the recipient.
Reference: 1. Roberta Callus, Jesmar Buttigieg, Andrei Agius Anastasi, Ahmed Halawa. Basic concepts in kidney transplant immunology British Journal of Hospital Medicine, January 2017, Vol 78, No 1. 2. Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339.
What information do you need to know to support your decision?
The current status of the donor needs to be known … the hemodynamic condition, amount of blood loss from the accident (if any), biochemical parameters and urine output (within the ICU). In addition, we need to know the blood group of both the donor and the recipient as well as the presence of any active infections.
Will you accept this offer and go ahead with the transplantation?
Yes, we may proceed with the transplantation if there are no absolute contraindications. There is 000 mismatch and there is no DSA – the chance of rejection is low. We also need to ensure that the primary disease of the recipient is controlled – so that the graft does not fall victim to the systemic insults that has been damaging the native kidneys of the patient.
What is meant by virtual crossmatch? What are the pros and cons?
Unlike a physical crossmatch or PXM, a virtual crossmatch or VXM involves comparing and matching (on pen and paper or computer software) between the HLA Antigens of the donor and the HLA Antibodies of the recipient to analyse whether they may cross-react if this donor kidney is transplanted to this recipient.
PROs
Only the HLA Antigen Typing and HLA Antibody Profile is needed. Transport of donor kidney or blood physically to the location of the recipient for physically cross-matching is not necessary.
VXM reduces the hassle of transport and thus the time wasted in performing the cross-match. In case of deceased donors, this shortens the cold ischemia time and improves graft outcome.
Reduces the cost of performing PXM multiple times with multiple possible donors for highly sensitized recipients.
CONs
A special lab method using solid-phase single antigen bead (SAB) technology is preferred for detecting presence of HLA antibodies. This is not widely available.
Often false positive and false negative results are found; ie in vitro the physical crossmatch result may differ with the VXM. And also in vivo the recipient’s immune system may behave differently with the transplanted kidney.
Presence of antibodies in the recipient not identified by the serum test or presence of donor antigens not included in HLA typing may lead to graft rejection if PXM is not done.
Reference:
Jaramillo, Andrés PhD1; Reddy, K. Sudhakar MBBS2; Heilman, Raymond L. MD3. Using the Virtual Crossmatch to Allow for Safer and More Efficient Kidney Transplantation of Highly Sensitized Patients. Transplantation 104(6):p 1121-1122, June 2020. | DOI: 10.1097/TP.0000000000002925
What information do you need to know to support your decision?
– ABO compatibility.
– HLA compatibility
– Any History of sensitizing events for both donor and recipient.
– Recent anti-HLA antibodies profile for the recipient.
– Virtual cross matching.
– Virology screening CMV, EBV, HIV.
Will you accept this offer and go ahead with the transplantation?
Yes, this donor can be accepted as is a good match and no DSA.
What is meant by virtual crossmatch? What are the pros and cons?
– VXM is a risk assessment tool, determine the immunologic compatibility between a recipient and a donor by analyzing and comparing the results of 2 independently done laboratory tests—patient anti-HLA antibody and donor HLA typing.
-can predict actual crossmatch results based on antibody specificity and strength detected by solid-phase assays.
-need an up-to-date HLA antibody testing of recipients and complete HLA typing of donors for accurate predictive results.
Pros:
– It improved organ allocation efficiency.
– Define unacceptable antigens
– Reduced testing costs.
– Shorter wait times and cold ischemia time
– more sensitive than PXM to detect the presence of DSA.
– Does not require a viable cell.
– a possible positive crossmatch is a risk factor for donor selection.
Cons:
– The use of antibody specificity from historical sample (earlier than 6 months) could not predict a crossmatch with certainty.
– False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies or denatured human leukocyte antigen on SAB.
– The result varies according to the laboratory’s MFI cutoff values
– False negative results due to:
– the list of all potential HLA donor antigen, cannot be correctly represented.
– HLA structure present on the SAB assays differs between the 2 vendors that are currently available
– Shared epitopes.
– Inhibitory factors present in the patient serum may interfere with antibody detection (prozone effect).
– VXM does not identify the HLA “Null” alleles.
Reference:
Human leukocyte antigen typing and crossmatch: A comprehensive review Mohammed Mahdi Althaf, Mohsen El Kossi, Jon Kim Jin, Ajay Sharma, Ahmed Mostafa Halawa World J Transplant 2017 December 24; 7(6): 276-363
What information do you need to know to support your decision?
– ABO compatibility
– Present DSA
– History of presensitization (pregnancy, blood transfusion)
– History of donor i.e- H/O malignancy, DCD or DBD
Will you accept this offer and go ahead with the transplantation?
If there is ABO compatibility i will accep this donor as there is 000 mismatch, no DSA and negative VXM.
What is meant by virtual crossmatch? What are the pros and cons?
– VXM is a risk assessment tool, determine the immunologic compatibility between a recipient and a donor by analyzing and comparing the results of 2 independently done laboratory tests patient anti-HLA antibody and donor HLA typing. -A virtual crossmatch can predict actual crossmatch results based on antibody specificity and strength detected by solid-phase assays.
PROS
– Quick (shorter wait times) – Tests against a large number of fixed and consistent HLA antigens – Can be performed at the time of donor identification – Consider a potentially positive crossmatch depending on a risk factor for donor selection
CONS – Does not identify the HLA “Null” alleles (are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface).
– The use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty – False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies – False negative results due to the fact that the list of all potential HLA donor antigens have been classed differently -The results from are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well
What information do you need to know to support your decision?
1- Blood group for both donor and recipient .
2- viral status for both the donor and recipient
3- History of sensitization ( blood transfusion , pregnancy .. etc )
4- We have to do vXM
5- History of previews infection or malignancy .
Will you accept this offer and go ahead with the transplantation?
Yes I will accept this donor , 0 0 0 MM with No DSA
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch involves comparison of recipient’s anti-HLA antibody profile with the HLA antigens of the prospective donor. If the recipient is not sensitized against the donor, transplantation can be done without a final FCXM. Pros: 1- quickens the transplantation process and reduces costs. 2- acceptable recipients are quickly identified, 3- cold ischemia time is reduced, 4- unnecessary graft shipments are avoided 5- the chance that a recipient with high sensitization gets transplanted is increased cons : 1- false negative result if DSA against a rare allele is present 2- Given its high sensitivity, L-SAB can also detect clinically unimportant DSA, leading to some recipients missing the chance to be transplanted. 3- the prediction of a positive FCXM by vXM is affected by the MFI value used and the DSA type
References
1) Crossmatching in Renal Transplantation by Non-Immunologists for Non-ImmunologistsMartin Chari,1,2 Mohsen El Kosi,2,3 Jon Kim Jim,2,4 Ajay Sharma,2,5 Ahmed Halawa2,62) Hand book of kidney transplantation 6th edition
What information do you need to know to support your decision?
· ABO group of donor and recipient · cadaver donor type – DBD/DCD; vitals and last ser creatinine before retrieval; cold ischemia time since retrieval · viral serology of donor & recipient (HIV, Hepatitis B&C, CMV, EBV) · Recipient’s clinical details: o cause of CKD; infections and malignancies o h/o sensitization (blood transfusion, pregnancy, previous transplant)– · HLA typing of donor and recipient; · Complete antibody – SAB assay (by Luminex-NGS) report of recipient, preferably with in last 3 months. · C-PRA % of the recipient · Virtual crossmatching – as blood / tissue of donor not available
Will you accept this offer and go ahead with the transplantation?
34Years young donor, no significant past medical history, excellent kidney function, 000 mismatch, no DSA – the offer is well acceptable for this recipient. We should go ahead with the transplant, provided the organ is well preserved and within the allowable cold ischemia time.
What is meant by virtual crossmatch? What are the pros and cons?
VIRTUAL CROSSMATCHING:
· The VXM is defined as “An assessment of immunologic compatibility based on the patient’s alloantibody profile compared to the donor’s histocompatibility antigens”.
· It is a very specific assessment for donor-specific anti-HLA antibody sensitization by combining the HLA typing of the donor with the detailed antibody profile (solid phase assy, preferably Single Antigen Beads analysis) of the recipient to determine HLA compatibility.
· In contrast to a physical crossmatch (donor cell-based CDC / Flowcytometry) methods, the VXM does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment (SAB assay) of the recipient, may be done in 2 different labs in different time.
· Thus, the VXM can be performed in minutes which allows for faster transplant decisions thereby increasing the likelihood that organs can be shipped across significant distances yet safely transplanted.
Pros (Advantage): VXM has a significant advantage over physical crossmatching
· It has been acceptable as the only pretransplant “crossmatch” necessary in many studies · Avoid unnecessary delay in physical crossmatching (cumbersome and time taking in transporting donor sample to the recipient’s centres for testing), hence shortens the cold ischemia time – avoid wastage of organs, improve clinical outcome in recipients. Sometimes adequate donor samples may not be available for test in subsequent labs, if the first recipient does not match with.
· Increased sensitivity/ ability to detect donor-specific HLA antibodies increase donor pool and more likelihood of finding compatible donors for highly reactive patients
· Allow successful transplantation of more dialysis patients who are highly sensitized to HLA allo-antigens – increase transplant accessibility and reduce time on waiting list · Improves risk assessment for transplant rejection, thus can plan suitable induction and immunosuppression protocol
Cons (disadvantages) of VXM) · Requires coordination between the immunology lab and the transplant team
· denatured antigens, nonexposed epitopes, or bead abnormalities not excluded, can lead to false positive VXM · MFI cut-off for positivity is not consistent in different lab / methods · The antibody profile can change with time, so wait-listed patients need to have repeat SAB /DSA profile done every 3months · More costly References: 1. Morris AB, Sullivan HC, Krummey SM, et al. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era. HLA 2019 Dec; 94(6): 471-481. 2. Bhaskaran MC, Heidt S, Muthukumar T, et al. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney International Reports 2022 Jun; 7(6): 1179-1188.
What information do you need to know to support your decision?
I would information regarding
Recipient HLA antibodies (by SAB assay within 3 months of transplant)
Donor HLA typing by DNA method probably till 2nd level
Sensistization history in the recipient (previous transplant, blood transfusions, pregnancy)
cPRA levels
Will you accept this offer and go ahead with the transplantation?
Yes, I would go ahead with this transplant, provided the virtual cross match is negative.
If this recipient has not sensitization history and if cPRA is low, then the transplant can proceed provided the virtual crossmatch is negative.
What is meant by virtual crossmatch(VXM)? What are the pros and cons?
The American Society for Histocompatibility and Immunogenetics defines VXM test as an assessment of immunologic compatibility based on patient’s alloantibody profile compared with donor’s histocompatibility antigens.
pros:
It significantly decreases cold ischemia times which are predictors of graft survival.
Several transplant centers have reported their success with proceeding to transplant based on VXM results and eliminating pretransplant PXM
A recent analysis of US registry data identified 9632 kidney transplants between 2011 and 2018 using VXM and 71,839 using PXM.42 Cold ischemia time was significantly lower in the VXM group (mean 15.0 hours) compared with the PXM group (mean 16.5 hours).
Importantly, mortality and death-censored allograft failure were similar.
cons:
The test may not be correct in two circumstances
Recipient antibodies
limitations of the SAB assay—in defining the absence or presence of circulating antibodies against HLA.
For example,
(i) the SAB assay may not contain beads for a particular specificity;
(ii) SAB manufacturing issues result in lot-to-lot variability
(iii) HLA structure present on the SAB assays differs between the 2 vendors that are currently available;
(iv) shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen
(v) inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect) and require pretreatment of serum with heat, dithiothreitol, or ethylenediamine tetra-acetic acid, or dilution of the serum.
All these could result in false-negative result (DSA present but reported as negative in the SAB assay)
Donor HLA typing
sensitive SAB assays are able to identify antibodies in the prospective recipient against HLA at field 2 resolution (when listing a patient’s unacceptable antigen, UNet [organ transplant web platform in the United States] allows reporting of HLA at field 2 rather than field 1), because prospective donor genotyping is mostly reported at field 1 resolution, this creates a challenge in the interpretation of HLA compatibility and in decisions on organ allocation
other con would cost and practicality of performing the recipient antibodies every three months.
Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
Q 1.What information do you need to know to support your diagnosis?
I will be needing information about,
1. HLA typing,
2. Blood grouping,
3. Virtual cross match report,
4. Viral serology report,
5. The cause of renal failure in recipient,
6. Previous transplantation,
7. DSA level.
Q 2. Will you accept this offer and go ahead with the renal transplantation?
I will accept this donation as there is no such high risk and contraindication.
Q 3. What is meant by virtual cross-match and what are pros and cons?
The virtual cross-match is the process of assessing the result of solid phase and cell based HLA antibody identification assays to predict the result of physical cross-match.
In contrast to physical cross-match, the virtual cross-match does not need viable donor cells but relies on complete HLA typing of the donor and current antibody assessment of the recipient.
What information do you need to know to support your decision?
(i) ABO blood group of pair
(ii) Virtual cross match should be done
(iii) History of any chronic illnesses, malignancies
(iv) HLA typing of recipient and anti HLA Ab testing
(v) Flow cytometry of B and T lymphocytes
(vi) Any risk of sensitization eg. blood transfusion, pregnancies
(vii) Viral screening: HIV,CMV,EBV
Will you accept this offer and go ahead with the transplantation?
I shall accept this donor as 000 HLA miss match, excellent kidney function , and absence of DSA, I shall go for ABO compatibility and virtual cross match before transplant.
What is meant by virtual crossmatch? What are the pros and cons?
In this process comparing the recipient antibody from solid phase testing to the donor HLA typing as a prediction of the actual crossmatch.
Predicts presence of donor specific antibodies using solid phase without an actual crossmatch, three monthly collection of sera is done for antibody screening via solid phase assay to ensure the right anti HLA profile at the time of transplantation. Compares recipients’ HLA ab to donor HLA type to predict cross match result.
What are the pros of virtual crossmatch:
(i) Decreased investigation cost
(ii) Shortening of cold ischemic time
(iii) Facilitates kidney paired donation
(iv) The virtual crossmatch ensures timely allocation of organs
What are the cons of virtual crossmatch:
(i) Denatured HLA on single antigen beads is done and which may lead to a false positive result
(ii) Requires more coordination between immunologist and transplant team.
(iii)Is not a cent percent accurate and an actual crossmatch be performed as well. Reference:
1. Roberta Callus, Jesmar Buttigieg, Andrei Agius Anastasi, Ahmed Halawa. Basic concepts in kidney transplant immunology British Journal of Hospital Medicine, January 2017, Vol 78, No 1.
2. Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339.
What information do you need to know to support your decision
Deceased kidney donor
We must to know if it is DBD / DCD
Time of ischemia
Blood group cross match cPRA and HLA Typing
infections Hepatitis CMV,EBV ….
Full assessment of the Recipient including cardiac assessment,chronic infection including hepatitis,TB,EBV CMV
Repeating Blood group cross match cPRA HLA typing DSA
Will you accept this offer and go ahead with the transplantation?
Yes , I will accept such young deceased donor with 000 mismatching and excellent kidney function
What is meant by virtual crossmatch? What are the pros and cons?
Virtual Crossmatch is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch.
The virtual crossmatch does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient. Thus, the VXM can be performed in minutes which allows for faster transplant decisions thereby increasing the likelihood that organs can be shipped across significant distances yet safely transplanted.
Virtual crossmatch (VXM) analysis included serological and epitope identification. The serological analysis compared the serological HLA typing and antibody detection to identify the serological donor-specific antibody (sDSA).
I would like to know Blood group of donor and recipient Any recent sensitization event for recipient. I will accept this offer as 000 mismatch , No DSA The term “virtual” crossmatch refers to a process in which the clinician or laboratorian uses the results of two actual laboratory tests (the anti-HLA screening results and the HLA type of the donor) to deduce what the result of an actual crossmatch might be, should one be performed. If a candidate is found to have antibody against an HLA antigen for which the donor is mismatched with the candidate (DSA), and if the “strength” of the antibody is thought to be sufficient, there is some predictive value with a positive or negative actual crossmatch. The correlation of this DSA or “virtual crossmatch” naturally depends upon what kind of crossmatch is anticipated.(up to date)
What information do you need to know to support your decision?
Blood group and ABO compatibilitycrossmatch for the recipient – CDC and Flow XMLuminex- SAB for Anti-HLA Ab.Virological screening : HIV, Hepatitis , Syphilis ,CMV, EBV, VZVscreening for current active infectionsStructural assessment such as ultrasonography of kidneys and CTA 6 for donor,Will you accept this offer and go ahead with the transplantation?
Young Donor and no mismatches 000 HLA, good kidney function and absence of DSA. I will accept this donor.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch can now predict actual crossmatch results based on antibody specificity and strength detected by solid phase assays.
Pros
significantly improved organ allocation efficiencyreduced testing costsreduced cold ischemia timereduced time needed for testing after the organ arrives at the transplant centerfacilitated kidney paired donation (KPD) programsCons
Can give a false positive or negative result.Does not identify an HLA (Null) alleleAccurate prediction relies heavily on up-to-date HLA antibody testing of recipients and complete HLA typing of donors including HLA-A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPA1, and DPB1.
What information do you need to know to support your decision?
· Blood grouping
· CDC Cross match
· Flow cytometry cross match
· History of sensitization
· Viral screen including Hep B& C , HIV, CMV, Herpes Simplex
Will you accept this offer and go ahead with the transplantation?
Yes , I will accept this offer subject to DSA levels.
What is meant by virtual crossmatch? What are the pros and cons?
Physical crossmatch tests, such as complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FCXM), require mixing of patient serum and donor cells, are labor intensive, and are logistically challenging.
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing. The goal of VXM is pretransplant risk stratification.
The Pros
Sensitivity similar to FXCM
Less ischemia time
Less risk of hyperacute rejection and early ABMR
Detection of acceptable and unacceptable antigens
The Cons
False positive results can happen
False negative due to incomplete HLA typing of donor and DSA in recipient against Epitope not available on SAB
Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348
What information do you need to know to support your decision?
ABO compatibility between donor and recipient.
Prior sensitisation episodes in the recipients.
Cause of the CKD.
Virology status-HepB, HepC, HIV, CMV
HLA typing
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept young donor no cross match and no DSA. Proceed with virtual cross match.
What is meant by virtual crossmatch? What are the pros and cons?
VXM applies the assessment of immunological compatibility between donor and recipient by use of 2 independently physically done patient anti-HLA antibody and donor HLA typing.
Pros: Shorter waiting time and improved outcomes for sensitised patients.
Cons: False positive results can occur when there are low titers or non-complement binding antibodies. False negative can occur when the list of all potential donor HLA antigens are classified differently thus incorrectly represented. VXM are not 100% accurate and should thus be followed by actual crossmatch. VXM does not identify null HLA alleles.
References
Human leukocyte antigen typing and crossmatch: A comprehensive reviewMohammed Mahdi Althaf, Mohsen El Kossi, […], and Ahmed Mostafa Halawa
Principles of Virtual Crossmatch Testing for Kidney Transplantation
Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani Muthukumar4,5
It is a highly specific cross match method used in deceased donor transplantation.
It didn’t need a tissue to get accurate cross match result.
It depend on donor HLA typing & solid phase antibody screen together.
Advantages:
reduce waiting time & improve outcome of sensitized patients.
highly accurate.
improve organ allocation efficiency
reduced test cost.
reduce cold ischemia time.
Disadvantage:
Titer, specificity, & presence or absence of antibodies can vary over time.
need determination of sensitization status (pregnancy, blood transfusion & previous transplantation).
doesn’t identify null allels.
False negative result occur in significant low level of Abs & non complement bind Abs.
false negative result can occur if the list of donor antigen classed differently.
References:
Danovithch. Handbook of Kidney Transplantation. 6th edition.
Althaf M., El Kossi M., Jin J., Sharma A. and Halawa A. Human luekocytes antigen typing and crossmatch: A comprehensive review. World J Transplant, 2017; 7(6):339-348.
What information do you need to know to support your decision?
blood grouping and virtual cross match and CDC.
sensitization event in the recipient sus as blood transfusion and previous transplant.
virology screening such as hepatitis B.C.HIV.EBV and CMV.
any previous PRA%.
any previous crossmatching.
any history of malignancy.
Will you accept this offer and go ahead with the transplantation?
yes will proceed for transplantation as 000 mismatches and there is no DSA if no contraindication for renal transplant
What is meant by virtual crossmatch? What are the pros and cons?
virtual crossmatch test assesses immunological compatibility between the recipient and potential donor by analyzing the result of two independently done physical laboratory tests, patient, anti-HLA antibody, and donor HLA typing
What is meant by virtual crossmatch? What are the pros and con
advantage of FXM reduce the cold ischemia time without an increase in hyperacute rejection.
allowed more organ transplantation for sensitized kidney transplant recipients when has no physical cross-matching before transplantation.
aid detection for preexisting antiHLA antibodies by luminx and ELISA.
disadvantage:
has some missing information such as certain alleles.
false positive and false negative result;
missing presence of some antibodies not detected by virtual cross-match that presence in the serum or donor antigen not detected by HLA typing so leads to graft rejection.
References
41. Aslam S., Buggs J., Wyatt K., et al. The impact of virtual crossmatch on cold ischemic times and outcomes following kidney transplantation. Ann M Surg. 2021;87:109–113. doi: 10.1177/0003134820942180. [PubMed] [CrossRef] [Google Scholar]
42. Puttarajappa C.M., Jorgensen D., Yabes J.G., et al. Trends and impact on cold ischemia time and clinical outcomes using virtual crossmatch for deceased donor kidney transplantation in the United States. Kidney Int. 2021;100:660–671. doi: 10.1016/j.kint.2021.04.020. [PMC free article] [PubMed] [CrossRef] [Google Scholar]
Null allels : some allels with gene mutation contain sequence defects preventing normal antigen expression on cell surface. They are non immunogenic and of less significance in solid organ transplantation.
In case of deceased donor transplantation, we perform VXM. Donor HLA typing is requiredand recipient solid phase assays as well.
-DSA may change due to sensitization so Luminex SAB should be repeated / 3 months..
-Wet CM should be performed in sensitized patients considering possibility of new DSA, (positive FCXM, negative VXM).VXM could be enough in non-sensitized recipients.
1. What information do you need to know to support your decision?
-Blood group.
-Recipient HLA-Abs by SAB techinque
-Donor HLA-Ags Will you accept this offer and go ahead with the transplantation?
Yes,because 000 mismatches , no DSA and donor age is suitable for recipient What is meant by virtual crossmatch?
A test to determine the immunologic risk of a recipient with a potential donor by ensuring that there are no transplant-relevant circulating antibodies in the recipient directed against donor antigens. What are the pros and cons? Pros:
-It provides a quick assay for high-resolution HLA typing that is available for deceased donors. Cons:
– limitations of the SAB assay—in defining the absence or presence of circulating antibodies against HLA:
1.the SAB assay may not contain beads for a particular specificity .
2.SAB manufacturing issues result in lot-to-lot variability.
3.HLA structure present on the SAB assays differs between the 2 vendors that are currently available,
4. shared epitopes—antibody targets .
5. inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect) and require pretreatment of serum .
Thus, the failure to detect an antibody on a SAB assay is not a proof of absence of that antibody in circulation. Reference:
-Madhu C et al .Principles of Virtual Crossmatch Testing for Kidney Transplantation. NIH.2022 Mar 15. doi: 10.1016/j.ekir.2022.03.006
1-What information do you need to know to support your decision? the basic information after referral to organ procurement organization opo
Patient’s name, age, date of birth, sex, race, and medical record number
Patient’s admitting diagnosis
Ventilator status of the patient
Neurologic status of the patient
Plan for brain death testing
Patient’s current vital signs, labs, and medications
Patient’s past medical history
Family’s understanding of the patient’s event/status
Initial donor screening — The organ donor referral from a hospital will be initially screened to exclude obvious patients who cannot be donors.
Common screening questions include:
What is the age of the patient?
Is the patient currently on a ventilator?
Does the patient have an active malignancy or a history of malignancy?
Are brain death examinations planned?
Is the family ready to withdraw support?
Immediate contraindications to donation — The following patient characteristics are generally considered to be absolute contraindications to deceased organ donation:
Age >80 years
Not on a ventilator
History of active metastatic cancer
History of active hematologic malignancy
History of active melanoma
History of Creutzfeldt-Jakob disease
Routine blood and urine tests — The following laboratory tests are performed on all deceased donors:
Complete blood count
Serum electrolytes, blood urea nitrogen (BUN), and creatinine
Liver function tests
Urinalysis
Arterial blood gas (ABG)
Prothrombin time (PT)/international normalized ratio (INR) and activated partial thromboplastin time (aPTT)
Blood, sputum, and urine cultures
ABO blood typing ABO blood typing must be performed on two different blood samples, drawn at separate times, with congruent results. ABO subtyping must be performed on all donors with blood type A to determine if the blood type is non-A1, since blood type A, non-A1 donors (eg, blood type A2) can be used for low titer blood type B recipients. ABO subtyping can only be reported if there is congruence between the two samples. The blood type must be verified by two qualified health care professionals, with source documentation, and reported to UNOS prior to the match run.
Histocompatibility testing — All deceased donors must have human leukocyte antigen (HLA) typing of antigens A, B, Bw4, Bw6, C, DR, DR51/52/53, DQA1, DQB1, and DPB1. Many OPOs send the donor’s blood samples to a reference lab for HLA typing. However, if the donor is at an academic hospital or transplant center, HLA testing is typically performed at the institution’s tissue typing laboratory. The results must be available before any kidney or pancreas is offered to the transplant centers on the match run. The HLA results must be available before final acceptance of an offer for heart or lung donors, if required by the transplant program. The OPO provides donor blood or lymph nodes to the transplant centers for direct crossmatching for kidney donation
Infectious disease testing — All organ donors are tested for various infectious diseases that can be transmitted to a recipient. Infectious disease testing requirements include the following:
HIV antibody (anti-HIV) donor screening test or HIV antigen/antibody (Ag/Ab) combination test
HIV RNA nucleic acid amplification test (NAT)
Hepatitis B surface antigen (HBsAg) donor screening test
Hepatitis B core antibody (anti-HBc) donor screening test
Hepatitis B DNA NAT
Hepatitis C virus antibody (anti-HCV) donor screening test
Hepatitis C RNA NAT
Cytomegalovirus antibody (anti-CMV) donor screening or diagnostic test
Epstein-Barr virus antibody (anti-EBV) donor screening or diagnostic test
Syphilis donor screening or diagnostic test
Toxoplasma immunoglobulin G (IgG) antibody test
2-Will you accept this offer and go ahead with the transplantation?
NO
There was no blood sample or lymphoid tissues available to run the crossmatch. Histocompatibility testing — All deceased donors must have human leukocyte antigen (HLA) typing of antigens A, B, Bw4, Bw6, C, DR, DR51/52/53, DQA1, DQB1, and DPB1. Many OPOs send the donor’s blood samples to a reference lab for HLA typing. However, if the donor is at an academic hospital or transplant center, HLA testing is typically performed at the institution’s tissue typing laboratory. The results must be available before any kidney or pancreas is offered to the transplant centers on the match run. The HLA results must be available before final acceptance of an offer for heart or lung donors, if required by the transplant program. The OPO provides donor blood or lymph nodes to the transplant centers for direct crossmatching for kidney donation
3-What is meant by virtual crossmatch? What are the pros and cons?
is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of aphysical crossmatch. Based on this data review, donor organ offers can be accepted or declined based on the predicted risk of transplan
Virtual Crossmatching in Kidney Transplantation, Shiraz Experience in Development of a Web-Based Program2021Results: The average time for a manual VXM was 30 minutes per patient, while the virtual cross web-based program took 5 minutes per patient. In 12% of the manual VXM cases, a secondary review of data improved final results. In two manual virtual crossmatches, the VXM results had errors in matching recipient antibodies with the donor HLA typing that could affect the final decision for transplantation. Conclusion: In conclusion, a web-based VXM program that assesses HLA data can accurately perform a VXM with fewer human errors. It is especially true for highly sensitized candidates.
What information do you need to know to support your decision? · Blood grouping and crossmatch(CDC &FCXM) are needed. · History of blood transfusion and sensitization in regard to potential recipient. · Virology screening, including CMV, EBV, HIV, HSV, hepatitis B&C.
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept this offer provided no DSA and 000 mismatch.
What is meant by virtual crossmatch? What are the pros and cons? Virtual crossmatching refers to the comparison of the anti-HLA antibodies of the recipient, as defined by Luminex, with the HLA of the donor. Antibodies are defined against HLA class I and II antigens(1). Virtual crossmatching ;the pros and cons(2) the pros · This technique is as sensitive as flow crossmatching and provides the specificity of the antibody. · One advantage Luminex testing has over other forms of crossmatching is the removal of false positives because of antibody binding to non-HLA antigens. · Confusion regarding the class of HLA they are binding to is eliminated. The cons
Luminex testing has some limitations including: · VXM is less predictive for CDCXM because the latter measures complement-dependent cytotoxic function. VXM predictability is better for positive/negative FLXM than for positive/negative CDCXM results to evaluate a single HLA-A, B, -DR DSA. · Possible interference of the assay by IgM. · Incomplete antigen representation on bead sets.
· Variation in HLA density on beads.
References 1. Bielmann D, Honger G, Lutz D, Mihatsch MJ, Steiger J, Schaub S. Pretransplant risk assessment in renal allograft recipients using virtual crossmatching. Am. J. Transplant. 2007; 7 (3): 626.Review Article 2. WILLIAM R MULLEYand JOHN KANELLIS1Understanding crossmatch testing in organ transplantation: A case-based guide for the general nephrologist Nephrology 16 (2011) 125–133
What information do you need to know to support your decision?
I need to know the primary disease of the recipient that lead to ESRD, previous history of sensitization like multiple pregnancies blood transfusion, and previous KTX
Any historic or previous positive crossmatch Will you accept this offer and go ahead with the transplantation?
We need to do virtual crossmatch, Acceptable time frames for sera used for virtual crossmatches<30 days for sensitized patients and >30 days for unsensitized patients). as the conventional physical crossmatch like CDCXM and FCXM is not possible and needs the mixing of patient sera with donor cells and this will prolong the cold ischemia time and increase the risk of IRI and DGF while the VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a potential crossmatch strategy, VXM by principle used shorter wait times and better outcomes for sensitized transplant recipients The speed of results produced allows a VXM to be performed at the time of donor identification. If no previous history of sensitization, no previous positive crossmatch, and no DSA yes will consider her for TX What is meant by virtual crossmatch? What are the pros and cons?
VXM may be applied for both sensitized and non-sensitized patients. immune compatibility is assessed by
analyzing the results of donor HLA typing and patient antibodies against HLA. Application of VXM is possible both at the time of
organ allocation and after organ allocation. At organ allocation, the process of listing unacceptable antigens by CPRA % or acceptable mismatches for a given patient and organ allocation based on that listing is equivalent to a negative VXM result. The antibody profile is used for predicting compatibility with prospective donors.
Implementation of the VXM-based approach has resulted in a statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes.
False positive results of VXM may arise where there are significantly low titer and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors
(1). The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.[VXM does not identify the HLA “Null” alleles. (1).More cost with VXM References
1. Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348. doi: 10.5500/wjt.v7.i6.339. PMID: 29312863; PMCID: PMC5743871.
2. Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
What information do you need to know to support your decision?
I need to know the primary disease of the recipient that lead to ESRD, previous history of sensitization like multiple pregnancies blood transfusion, and previous KTX
Any historic or previous positive physical crossmatch, the CPRA %
Will you accept this offer and go ahead with the transplantation?
We need to do virtual crossmatch as the conventional physical crossmatch like CDCXM and FCXM are not possible as we need the mixing of patient sera with donor cells and this will prolong the cold ischemia time and increase the risk of IRI and DGF while the VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a potential crossmatch strategy, VXM by principle used shorter wait times and better outcomes for sensitized transplant recipients The speed of results produced allows a VXM to be performed at the time of donor identification.
What is meant by virtual crossmatch? What are the pros and cons?
VXM may be applied for both sensitized and non-sensitized patients. immune compatibility is assessed by
analyzing the results of donor HLA typing and patient antibodies against HLA. Application of VXM is possible both at the time of
organ allocation and after organ allocation. At organ allocation, the process of listing unacceptable antigens by CPRA % or acceptable mismatches for a given patient and organ allocation based on that listing is equivalent to a negative VXM result. The antibody profile is used for predicting compatibility with prospective donors.
Implementation of the VXM-based approach has resulted in a statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes.
False positive results of VXM may arise where there are significantly low titer and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors (1). The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.VXM does not identify the HLA “Null” alleles. (1) and its more expensive assay compared to conventional crossmatch. References
1. Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348. doi: 10.5500/wjt.v7.i6.339. PMID: 29312863; PMCID: PMC5743871.
2 Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
1. 1. Choose the correct answer regarding Null HLA alleles A. It could be missed on VXM B. It is unexpressed HLA but identified by molecular testing C. More important in renal transplantation D. DSA against unidentified null alleles can cause an immunological challenge E. All the above Answer: ABD
A VXM does not identify ‘null alleles’, which have DNA sequences identifiable on molecular typing but do not express HLA on the cell surface. In such a scenario, the donor null allele can be identified as a fully expressed product by the recipient, and DSA can develop in the recipient leading to difficulties in future transplantation. It will have no effect if the recipient expresses the antigen.
2. Choose the correct answer regarding VXM A. Needs regular monitoring of the DSA profile of potential recipients on the waiting list B. Needs full HLA A, HLA B and DR typing ONLY C. Is more expensive than wet crossmatch D. Needs sensitisation history (pregnancy, blood transfusion, etc.) E. All the above Answer: AD
VXM is done in deceased donor transplantation, to perform VXM we need to have donor HLA typing and recipient solid phase assays (ELISA or bead assay- luminex)
DSA may change over time due to sensitization from a blood transfusion or pregnancy so luminex SAB should be repeated every 3 m.
Wet cross-match should be performed in only sensitized patients as there may be a new DSA that develop, this should be detected by wet cross match (positive FCXM, negative VXM), in non-sensitized recipient we can rely on VXM in proceeding with transplantation.
NB I have collected the explanation of the answers from Amit Sharma and Sherif Yousef’s replies
◇ What information do you need to know to support your decision?
▪︎ I need to know blood grouping and if there is any history of sensitization (pregnancies, previous transplant or blood transfusions).
◇ Will you accept this offer and go a head with the transplantation?
▪︎If there is no risk I will accept it, because the HLA mismatches is good and the DSA is negative, so this carry low immunological risk.
◇ What is meant by virtual crossmatch? ▪︎Virtual Crossmatch is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch.
▪︎Based on this data review, donor organ offers can be accepted or declined based on the predicted risk of transplant.
▪︎Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory test (patient anti-HLA antibody and donor HLA typing).
▪︎The goal of VXM is pretransplant risk stratification (1).
◇ What are the pros and cons of virtual crossmatch:
¤ Pros: 1. It can permit import of organs from outside the local organ procurement area for very highly sensitized kidney recipients when a physical crossmatch is not performed prior to transplant (1).
2. VXM may be applied at different scenarios—both for sensitized and nonsensitized patients.
3. Implementation of VXM-based approach has resulted in statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes.
4. The solid-phase assays, including ELISA or multiple beads–based technology (Luminex) can allow an accurate detection and characterization of preexisting anti-HLA antibodies .
5. It decreases the workload in HLA-laboratories and facilitates the organ allocation even in sensitized recipients.
6. the virtual crossmatch does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient (2).
7. It is a safe and efficient way of selecting kidney transplant recipients.
8. It reduces the time kidneys were kept on ice while awaiting identification of a suitable recipient,improved scheduling for surgeons and operating room staff, and alleviated emotional and logistical stress on patients who were called to the hospital only to be sent home hours later after a more suitable recipient was identified (3).
9. VXM using epitope analysis has the advantage of information from high-resolution HLA typing and the LSAB assay and can determine the donor epitope-specific antibody (eDSA) (4).
¤ Cons:
1. Unlike the donor cells used in the PXM, which contains the complete donor HLA repertoire, the LSAB assay usually contains only about 100 HLA alleles for each class, resulting in missing information for certain alleles, especially for common alleles that occur non-western populations.
2. A special labaoratorues which use solid-phase single antigen bead (SAB) technology are not available.
3. The presence of sDSA may be overestimated(4).
4. Because of the high sensitivity of the techniques and because of different current principles that are used in different laboratories to assess the presence of cytotoxic antibodies, some concerns have been expressed related to the ability to predict “true positive” crossmatches in the clinical scenarios. Several studies investigated the predictive value of the virtual-XM and conflicting results have been achieved. At the moment there are no consensus protocols available (5).
________________________
References:
(1)Bhaskaran, Sebastiaan Heidt, et al. Principles of Virtual Crossmatch Testing for Kidney Transplantation. C. Reports, 2022,. 1179-1188
(2) modern era Anna B. Morris, et al. Out with the old, in with the new: Virtual versus physical crossmatching.
(3) Virtual crossmatching improves quality of life for kidney transplant patients.
(4)Bo Peng, Quan Zhuang, et al. Comparison of Physical Crossmatch and Virtual Crossmatch to Identify Preexisting Donor-Specific Human Leukocyte Antigen (HLA) Antibodies and Outcome Following Kidney Transplantation.
(5) Moise A, Baston et al. Challenges and Clinical Significance of Virtual Crossmatch in Kidney Transplantation: Our Experience. SM J Urol. 2017; 3(3): 1032.
What information do you need to know to support your decision? The current status of the donor needs to be known … the hemodynamic condition, amount of blood loss from the accident (if any), biochemical parameters and urine output (within the ICU). In addition, we need to know the blood group of both the donor and the recipient as well as the presence of any active infections.
Will you accept this offer and go ahead with the transplantation?
Yes, we may proceed with the transplantation if there are no absolute contraindications. There is 000 mismatch and there is no DSA – the chance of rejection is low. We also need to ensure that the primary disease of the recipient is controlled – so that the graft does not fall victim to the systemic insults that has been damaging the native kidneys of the patient.
What is meant by virtual crossmatch? What are the pros and cons?
Unlike a physical crossmatch or PXM, a virtual crossmatch or VXM involves comparing and matching (on pen and paper or computer software) between the HLA Antigens of the donor and the HLA Antibodies of the recipient to analyse whether they may cross-react if this donor kidney is transplanted to this recipient.
PROs
Only the HLA Antigen Typing and HLA Antibody Profile is needed. Transport of donor kidney or blood physically to the location of the recipient for physically cross-matching is not necessary.
VXM reduces the hassle of transport and thus the time wasted in performing the cross-match. In case of deceased donors, this shortens the cold ischemia time and improves graft outcome.
Reduces the cost of performing PXM multiple times with multiple possible donors for highly sensitized recipients.
CONs
A special lab method using solid-phase single antigen bead (SAB) technology is preferred for detecting presence of HLA antibodies. This is not widely available.
Often false positive and false negative results are found; ie in vitro the physical crossmatch result may differ with the VXM. And also in vivo the recipient’s immune system may behave differently with the transplanted kidney.
Presence of antibodies in the recipient not identified by the serum test or presence of donor antigens not included in HLA typing may lead to graft rejection if PXM is not done.
Reference: Jaramillo, Andrés PhD1; Reddy, K. Sudhakar MBBS2; Heilman, Raymond L. MD3. Using the Virtual Crossmatch to Allow for Safer and More Efficient Kidney Transplantation of Highly Sensitized Patients. Transplantation 104(6):p 1121-1122, June 2020. | DOI: 10.1097/TP.0000000000002925
What information do you need to know to support your decision?
Information needed to support the decision includes: Donor: Type (Deceased or living), blood group, HLA typing, viral serology. Recipient: Blood group, HLA typing, history of sensitizing events between after the most recent antibody screening recent (within last 3-6 months) c-PRA and DSAs, extensive pre-transplant work-up. Crossmatch: either physical (CDC, or flow-cytometry) or virtual cross match. In this clinical scenario, there was no tissue from the donor (like LNs or Spleen). So virtual cross match is the available option.
Will you accept this offer and go ahead with the transplantation?
I will accept this offer.
This is a low immunological offer with 000 mismatch, no DSAs, no medical history in the donor with excellent renal function.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual cross match is performed via a computer system without doing an actual crossmatch, however it requires complete HLA typing of the donor and the recipient in addition to recipient’ s anti-HLA antibodies by solid phase assay method. Antibodies against donor’s antigens will be considered as positive virtual cross match. Unsuitable donors can be excluded if the recipients have antibodies to their antigens. Pros: No need for viable donor cell Quick procedure. Reduces cold ischaemia time. Highly Accurate. Less expensive. Cons: False positive results can happen because of presence of non-complement binding antibodies.
Denatured HLA on SAB can lead to false positive results.
False negative VCM can happen with incomplete donor’s HLA typing and with recipient’s DSAs against HLA epitope that was not available on SAB panel.
Reference:
Uptodate.
Sánchez-Fructuoso AI, Marques M, Prats D, et al. Victims of cardiac arrest occurring outside the hospital: a source of transplantable kidneys. Ann Intern Med 2006; 145:157.
Amico P, Honger G, Steiger J, Schaub S (2009) Utility of the virtual crossmatch in solid organ transplantation. Curr Opin Organ Transplant 14: 656–661.
1- Information required:
ABO compatibility
2- As long as there is available HLA typing of the donor and solid phase assay of recipient anti- HLA antibodies with confirmed ABO compatiibility, we can accept the donor (virtual cross match)
3- virtual cross match:
means depending on comparing the available donor HLA typing and the solid phase assay of the recipient anti-HLA antibodies without the need to use the patient serum and the donor lymphocyte for cross match. Pros:
A virtual crossmatch can now predict actual crossmatch results.
The virtual crossmatch has significantly improved organ allocation efficiency, reduced testing costs and, in many cases, cold ischemia time by reducing uncertainty and the time needed for testing after the organ arrives at the transplant center.
Importantly, virtual crossmatch accuracy has facilitated kidney paired donation (KPD) programs that involve multiple transplant centers
Cons:
Requires more coordination between the immunology lab and the transplant team members
Denatured HLAs on single antigen beads may lead to false positive results
The antibody profile can change with time (false negative results)
References Handbook of kidney transplantation 6th edition.
2. Results of receipient HLA antibodies done by single antigen bead assay( SAB)_ Luminx. It should include all results and importantly the recent should be within 3- 6 months. This will allow performing virtual cross match since no samples are available to go for actual cross match.
3. If any sensitization event that occurs after the last results of antibodies( 3- 6 months).
2. Will you go with the Tx?
yes will go with the transplant, since the important clincally mismatches are 0 0 0 and there are no DSA. But important to make sure no further sensitization event after the last results of virtual cross match.
3.what is virtual VXM?
it doesn’t involve the mixing of receipient serum with donor lymphocytes. It involves utilising the donor HLA typing and solid phase assay results of receipient (specific and sensitive) to predict what could be the result of actual cross match.
Advantages:
VXM is best utilized in deceased organ transplants as it can decrease the waiting times in the list by identifying donors especially for those who are sensitised. It is quick and can be performed at the time of deceased donor availability and especially used when historical serum samples for actual cross match are not available in less than 6 months.
Disadvantages:
A. False positive results when titre of antibodies are low ( as SPA is very sensitive) or the antibodies are not complement dependent. False positive results lead to incorrect exclusion of potential donors.
B. False negative results when HLA ag are classified differently and this incorrectly represented.
C. VXM doesn’t detect Null alleles.Null alleles are alleles identified by DNA sequencing when using molecular typing to identify HLA Ag. They are not expressed as products on cell surface. When null alleles are not detected as in VXM it means that transplant is done with the donor having the non detected alles as this can lead to the developement of DSA in the future. This doesn’t carry the risk of humoral rejection and is well tolerated but can affect future transplant. Worth noticing that the effect of null alles is less marked in solid organ transplant than stem cell transplant .
We need patient cPRA regardless of zero mismatch confirmed by VXM .
I will accept the offer and go ahead of transplantion but a lot of missed information about the donor i sould be aware of,like her virology status , is it DCD kidney ,any chronic ilnesses , what is her nadir creatinine.
VXCM is virtual comaprison between patient HLA typing and his cPRA with the donor HLA typing, which now used for both living and cadaveric kidney transplant to faclitate the process of transplantion.not costly, no need for wet cross mtah if recpient HLA &cPRA are avialble , it shortens cold ischemia time for cadveric kidney transplant, it may have disadavntages like updated cPRA for the recpient every three month and to be aware of ensitizing events which may be missed if the recient list is not updated regulary by trransplant cordinators .
1. A 41-year-old CKD 5 female received a deceased kidney offer, 000 mismatch. There is no DSA. The donor was 34-year-old, died in a road traffic accident. No past medical history with excellent kidney function. There was no blood sample or lymphoid tissues available to run the crossmatch.
What information do you need to know to support your decision?
– ABO compatibility
– HLA typing
– Virtual crossmatching
– viral serology/ status for both donor and recipient i.e., CMV, EBV, HIV, hepatitis B, hepatitis C
– history of prior senstisation i.e., blood transfusion, pregnancy, previous transplant
– history of prior infections (e.g., tuberculosis) and malignancies
– cause of CKD in the recipient
– any personal or family history of diabetes, hypertension, kidney disease in the recipient
– donor type i.e., DBD, DCD
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept the offer and proceed with transplantation given the 000 mismatch, no DSA, excellent kidney function, young donor with no significant past medical history
What is meant by virtual crossmatch? What are the pros and cons?
A crossmatch test helps determine the immunologic risk of a transplant recipient against a potential donor.
It ensures that there are no circulating antibodies in the recipient that are directed against the donor antigens.
There are different types of crossmatch tests: –
· Physical crossmatch test (PXM)
· Virtual crossmatch (VXM)
e.g., complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FCXM)
They require mixing of the recipient’s serum and the donor cells hence are labor intensive and pose a logistics challenge.
It assesses the immunologic compatibility between the recipient and potential donor by analysing the results two physical laboratory tests done independently i.e., recipient anti-HLA antibody and donor HLA typing
It involves use of: –
· solid phase assays to detect circulating antibodies in the recipient directed against individual HLA
· DNA-based methods to type donor HLA specificities at a higher resolution
– Increased sensitivity/ ability to detect donor-specific HLA antibodies
– Improves transplantation access for highly sensitized patients
– Improves risk assessment for transplant rejection
– Can be performed with stored serum hence shortening the cold ischemia time
– Requires more coordination between the immunology lab and the transplant team members
– Denatured HLAs on single antigen beads may lead to false positive results
– The antibody profile can change with time
References
1. Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney international reports. 2022 Jun;7(6):1179-88. PubMed PMID: 35685330. Pubmed Central PMCID: PMC9171621. Epub 2022/06/11. eng.
2. Morris AB, Sullivan HC, Krummey SM, Gebel HM, Bray RA. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era. Hla. 2019 Dec;94(6):471-81. PubMed PMID: 31515937. Pubmed Central PMCID: PMC7341023. Epub 2019/09/14. eng.
3. Bray RA, Nolen JD, Larsen C, Pearson T, Newell KA, Kokko K, et al. Transplanting the highly sensitized patient: The emory algorithm. American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant Surgeons. 2006 Oct;6(10):2307-15. PubMed PMID: 16939516. Epub 2006/08/31. eng.
4. Callus R, Buttigieg J, Anastasi AA, Halawa A. Basic concepts in kidney transplant immunology. British journal of hospital medicine (London, England : 2005). 2017 Jan 2;78(1):32-7. PubMed PMID: 28067566. Epub 2017/01/10. eng.
·What information do you need to know to support your decision?
I need to know:
Detailed HLA typing & ABO-compatability
If any antibodies detected in the SAB assay
The recipient’s sensitisation history, including previous transplants.
=============================
·Will you accept this offer and go ahead with the transplantation?
Yes, if the recipient is defined as un-sensitized, I will proceed with only a virtual cross-match assessment, since no sample is available for physical XM in this scenario.
=============================
·What is meant by virtual crossmatch? What are the pros and cons?
The ASHI defines virtual crossmatch (VXM) test as an assessment of immunologic compatibility based on patient’s alloantibody profile compared with donor’s histocompatibility antigens.
Conventional physical crossmatch (PXM) tests, such as CDCXM & FCXM, require mixing of patient serum & donor cells, are labor intensive, & remain logistically challenging. VXM test uses the results of 2 independently done physical laboratory tests & does not involve mixing of serum & cells. Instead, immunologic compatibility is assessed by analyzing results of donor HLA typing & patient anti-HLA antibody.
The need for pretransplant PXM increases cold ischemia time, while cold ischemia time is significantly lower when VXM is applied.
If laboratories report VXM as positive whenever DSA is positive, then VXM is potentially more sensitive than PXM to detect the presence of DSA.
Challenges in the Routine Implementation of VXM Testing:
Although VXM is a risk assessment tool, there is no consensus on the goal of VXM—whether the risk assessment involves predicting the result of a PXM or the post-transplant outcome.
The higher sensitivity could result in a group of patients who have a positive VXM result but a negative PXM result. Such a scenario could mean a low burden of DSA or non–complement-fixing DSA (FCXM+ & CDCXM-).
There are multiple challenges due to limitations of the SAB assay—in defining the absence or presence of circulating antibodies against HLA:
SAB assay may lack beads for a particular specificity
Lot-to-lot variability of SAB beads
Shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen
Inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect) and require pretreatment of serum with heat, or dilution of the serum.
References
Madhu C. Bhaskaran, Sebastiaan Heidtand Thangamani Muthukumar, Principles of Virtual Crossmatch Testing for Kidney Transplantation, Kidney Int Rep (2022) 7, 1179–1188; https://doi.org/10.1016/j.ekir.2022.03.006
Chose the correct answer regarding VXM A. Needs regular monitoring of the DSA profile of potential recipients on the waiting list B. Needs full HLA A, HLA B and DR typing ONLY C. Is more expensive than wet crossmatch D. Needs sensitisation history (pregnancy, blood transfusion, etc.) E. All the above
A. TRUE: VXM integrates the donor’s molecular HLA typing with the recipient’s comprehensive antibody profile. B. FALSE:In contrast to a PXM, the VXM does not require viable donor cells but rather relies on complete HLA typing of the donor & current antibody assessment of the recipient. C. FALSE: VXM may be the only pretransplant “crossmatch” necessary. It reduces unnecessary crossmatching & increases the likelihood of finding crossmatch-compatible donors for highly reactive patients. D. FALSE E. FALSE
Choose the correct answer regarding VXM A. Needs regular monitoring of the DSA profile of potential recipients on the waiting list. (True) B. Needs full HLA A, HLA B and DR typing ONLY. (false) C. Is more expensive than wet crossmatch. True D. Needs sensitization history (pregnancy, blood transfusion, etc.). True E. All the above False
A: True. DSA profile should be done at least once in 3 months to get more accurate results of VXM
B. False. It is better to get full HLA typing as the DSA prifle will include antibodies against HLA other than A, B and DR also.
C True. Although VXM does not require any physical testing (just comparison of HLA typing of the donor with DSA profile of the recipient) the testing for HLA typing of the donor is costlier than the cost of wet crossmatch (assuming that the DSA profile was done historically).
D. False. Sensitization history is not relevant except if the sensitization event has taken place after the last DSA profile testing.
E. False
A: True. DSA profile should be done at least once in 3 months to get more accurate results of VXM B. False. It is better to get full HLA typing as the DSA prifle will include antibodies against HLA other than A, B and DR also. C False. VXM does not require any physical testing (just comparison of HLA typing of the donor with DSA profile of the recipient) , hence it does not cost anything while a wet crossmatch is a physical test which would require expenditure. D. True. Sensitization history relevant if the sensitization event has taken place after the last DSA profile testing. A wet crossmatch should be done in the event of a history of sensitization. E. False
A- True
as initiation of a virtual cross match protocol using solid phase histocompatibility techniques has significantly increased the access of sensitised patients ( prior transplant, pregnancy or blood transfusion history) for kidney transplant.
B- False
C-True ( more cost effective).
D- True.
E-False.
A. Regular monitoring of the DSA profile of potential recipients is needed (True) if there is a history blood transfusion or pregnancy. B. Needs full HLA A, HLA B and DR typing (False) as well as HLA C, and HLA DQ typing. C. Is more expensive than wet crossmatch (True) because HLA typing of all antigens of the donor and recipient’s anti-HLA antibody profile by SAB technology are expensive. D. Sensitisation history (pregnancy, blood transfusion) (True) is necessary to ensure the validity of the VXM. E. All the above (False)
_⭐⭐correct answer is A and D.
_Virtual cross match is done in deceased donor transplantation.
_it needs HLA typing of the donor and DSA in the recipient (by luminex single Ag bead).
_ It is easier and less expensive than wet cross match. However, frequent monitoring of DSA is required every 3 months.
Chose the correct answer regarding Null HLA alleles A. It could be missed on VXM B. It is unexpressed HLA but identified by molecular testing C. More important in renal transplantation D. DSA against unidentified null alleles can cause an immunological challenge E. All the above
C- YES There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation.
D- YES VXM does not identify the HLA “Null” alleles.
====================================================================
B- FALSE the null allele is misidentified as a fully expressed product and, therefore, transplanted with a donor bearing the expressed antigen.
True, as if the recipient null allele is misidentified as fully expressed product (by molecular typing), there is a risk of choosing a donor with the same expressed antigen, leading to the development of DSA in the recipient against that antigen after transplantation with subsequent increase in the risk of rejection. Serological typing can identify null alleles, and may avoid this problem.
B. It is unexpressed HLA but identified by molecular testing
True
C. More important in renal transplantation
False, as it is more significant in stem cell transplantation than solid organ transplantation
D. DSA against unidentified null alleles can cause an immunological challenge
C=> the risk of null alleles is misleading for its fully expressed in stem transplantation, however, the risk is lower in solid organ transplantation which leads to DSA formation but has no life threaten effect.
A- True.
as Null HLA alleles are non-functional alleles caused by genetic mutations could be missed by VXM and serological typing is recommended.
B- True.
C- False
has significant role in hematopoietic stem cell transplantation.
D-False
as Null HLA alleles produce no detectable antigens on the cell surface and can be recognised through a comparative examination of serological and DNA-typing or through family study.
E-False.
A. (TRUE) It could be missed on VXM if the HLA Typing not done via molecular sequencing. False representation of a donor’s null allele as an expressed allele will unfortunately prevent transplantation of a possible donor kidney with no antigens for that allele into a patient even if that recipient has anti-bodies to that antigen. B.(TRUE) It is unexpressed HLA but identified by molecular testing. Null alleles are not found on serologic testing. C.(FALSE) More important in renal transplantation. Actually it is only important in the special case where the null HLA allele is present in the recipient and the same HLA antigen is expressed on the donor kidney resulting in DSAs and rejection. D.(TRUE) DSA against unidentified null alleles can cause an immunological challenge. DSAs against expressed antigens of donor alleles by the recipient carrying non-expressing null alleles for the same HLA antigens can cause rejection and need plasmapheresis or other anti-rejection therapy. E.(FALSE)All the above
A & D 1/sequencing-based typing was deemed the best technique in reducing problems with ambiguities and null alleles. 2/ it can cause GVHD in stem cell transplant. less important in renal transplant
⭐ ⭐ correct answer is A, B and D
_Null HLA alleles are not expressed on cell surface, so can be missed in virtual cross match. However it can induce DSA that can cause immunological challenge
·What information do you need to know to support your decision?
I need to know:
Detailed HLA typing & ABO-compatability
If any antibodies detected in the SAB assay
The recipient’s sensitisation history, including previous transplants.
=============================
·Will you accept this offer and go ahead with the transplantation?
Yes, if the recipient is defined as un-sensitized, I will proceed with only a virtual cross-match assessment, since no sample is available for physical XM in this scenario.
=============================
·What is meant by virtual crossmatch? What are the pros and cons?
The ASHI defines virtual crossmatch (VXM) test as an assessment of immunologic compatibility based on patient’s alloantibody profile compared with donor’s histocompatibility antigens.
Conventional physical crossmatch (PXM) tests, such as CDCXM & FCXM, require mixing of patient serum & donor cells, are labor intensive, & remain logistically challenging. VXM test uses the results of 2 independently done physical laboratory tests & does not involve mixing of serum & cells. Instead, immunologic compatibility is assessed by analyzing results of donor HLA typing & patient anti-HLA antibody.
The need for pretransplant PXM increases cold ischemia time, while cold ischemia time is significantly lower when VXM is applied.
If laboratories report VXM as positive whenever DSA is positive, then VXM is potentially more sensitive than PXM to detect the presence of DSA.
Challenges in the Routine Implementation of VXM Testing:
Although VXM is a risk assessment tool, there is no consensus on the goal of VXM—whether the risk assessment involves predicting the result of a PXM or the post=transplant outcome.
The higher sensitivity could result in a group of patients who have a positive VXM result but a negative PXM result. Such a scenario could mean a low burden of DSA or non–complement-fixing DSA (FCXM+ & CDCXM-).
There are multiple challenges due to limitations of the SAB assay—in defining the absence or presence of circulating antibodies against HLA:
SAB assay may lack beads for a particular specificity
Lot-to-lot variability of SAB beads
Shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen
Inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect) and require pretreatment of serum with heat, or dilution of the serum.
References Madhu C. Bhaskaran, Sebastiaan Heidtand Thangamani Muthukumar, Principles of Virtual Crossmatch Testing
for Kidney Transplantation, Kidney Int Rep (2022) 7, 1179–1188; https://doi.org/10.1016/j.ekir.2022.03.006
A 41-year-old CKD 5 female received a deceased kidney offer, 000 mismatch. There is no DSA. The donor was 34-year-old, died in a road traffic accident. No past medical history with excellent kidney function. There was no blood sample or lymphoid tissues available to run the crossmatch. 1.INFORMATION NEEDED;
-Pairs blood group.
-Hx of any CA and treatment status.
-Hx of any chronic illnesses.
-During postmortem evaluate for any features of a granulomatous disease or lymphadenopathies.
-Any risk of sensitization – blood transfusion, pregnancies of previous transplantation.
-Viral infection screen status- HIV,CMV,EBV etc
2.WILL YOU ACCEPT THE DONOR AND PROCEED WITH TRANSPLANTAION?
Yes I will.
Favorable donor- 000 mismatch, No DSA..
A VXM will be done
3.WHAT IS VXM? PROS/CONS ?
VXM is a virtual or non physical analysis of anti HLA antibodies in recipients with donor HLA profile. It has a +VE predictive value of more than 85% and a -VE predictive value of 50%.3monthly collection of sera is done for antibody screening via solid phase assay to ensure the right anti HLA profile at the time of transplantation.
PROS.
-Increased sensitivity.
-Facilitates transplantation of highly sensitized recipients.
-Offers a better risk assessment for rejection.
-Done with stored sera thus decreases cold ischemia time.
-Detection of both acceptable and non acceptable AGs decreases shipping time of organs, less SX delays and also decreases the cold ischemic time.
CONS.
-Denatured HLA antigens on SAB and presence of null antigens may lead to false +VEs
-Needs better coordination between lab and transplant team.
-False negative results can be from ;Incomplete typing of donor, DSA in recipient sera from HLA epitopes not on SAB panel.
REF;
Ahmed Halawa et al ; Basic concepts of kidney transplant immunology’VL 78,10.12968/hmed.2017.78.1.32.British Journal of Hospital Medicine.
What information do you need to know to support your decision?
1- ABO Compatibility
2- V – XM Should always be done (blood from recipient for HLA typing)
3-HLA typing for recipient for sure
4– Luminex- SAB (single antigen bead testing ) for Anti-HLA Ab.
5- Flow XM (T and B Lymphocytes)
6-History of sensitization especially after last blood sample given by recipient
7- Virological screening : CMV, EBV, VZV , HBV,HCV, HIV
8- Any history of active infections/ malignancy in the donor.
Will you accept this offer and go ahead with the transplantation?
Because of Young Donor and (000 HLA MM ), Excellent kidney function , and absence of DSA ,I will accept this donor depending on the ABO and virtual cross match (VXM)
What is meant by virtual crossmatch? What are the pros and cons?
It is not a true crossmatch but rather comparing the recipient antibody from solid phase testing to the donor HLA typing as a prediction of the actual crossmatch.
Predicts presence of donor specific antibodies using solid phase without an actual crossmatch , compares recipient’s HLA ab to donor HLA type to predict Xmatch results its use in lieu of ‘wet’ crossmatch is on the rise
It required Complete tissue type of the donor (HLA A, B, C, DP, DQ, DR) , Complete tissue type of the recipient , Complete anti HLA antibody analysis of the recipient Requires recent blood: < 3m
What are the pros of VXM :
1-Decreasing Test cost
2- Shortening Cold ischemia time
3- Facilitate kidney paired donation
4- The virtual crossmatch ensures timely allocation of organs and increases the chance of transplantation in highly sensitized individuals.
What are the Cons of VXM :
1-Denatured HLA on single antigen beads may lead to a false positive result.
2-Requires more coordination between immunology lab personnel and transplant team.
3-are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
4-VXM does not identify the HLA “Null” alleles.
False positive:
1- very low titer (it detect Ab with MFI >1000 while actual cross match need MFI >5000 to be +ve)
2- allele specific antibodies (e.g., anti-body to DRB1*0401 but not other DRB1*04 alleles) which may unnecessarily exclude other DR4 donors.
3- identify null alleles that are not expressed as antigens on the cell surface but would be excluded by VXM based on typing alone.
Falsely negative:
-All potential HLA antigens in the population cannot be completely represented on solid phase tests , Care must be taken to ensure that the donor alleles are completely represented on the solid phase panel in order to report a negative VXM
Reference:
1- Basic concepts in kidney transplant immunology British Journal of Hospital Medicine, January 2017, Vol 78, No 1 Dr Roberta Callus, Dr Jesmar Buttigieg, ,Dr Andrei Agius Anastasi, Mr Ahmed Halawa.
2- Tinckam KJ. Basic histocompatibility testing methods. In: Chandraker A, editor. Core concepts in renal transplantation. New York: Springer Science + Business Media, LLC; 2012. pp. 21–42.
3- Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339.
A: We need to do a virtual cross-match (VXM), using donor HLA typing and solid-phase antibody screening. Help is to be used at the time of transplantation as in this case and in cases that need to reduce the waiting time of transplantation. It helps to do a cross-matching in a way other than prospective cross-match, given that flow cytometry is progressively advancing sensitivity and specificity. B: We can accept this donor based on his 000 miss-match and no DSA. C: VXM; itis good at time transplant cross-match, and it is very sensitive and more specific when using a recent serum sample. Can give a false positive or a false negative result. Does not identify an HLA (Null) allele, with a great risk of a non-identifiable allele, although is much lower in SOT. A false negative result may arise due to the fact that not all HLA antigens are presented correctly. False positive results may arise when there is an inadequate titer or non-complement binding antibody, resulting in a wrong exclusion of potential donors.
What information do you need to know to support your decision?
1-HLA typing
2-History of previous sensitization like pregnancy,blood transfusion,previous transplants
3-cross match result
4-DSA titer
5–viral study
Will you accept this offer and go ahead with the transplantation?
I will accept this donor as there is 000 mismatch and no DSA
What is meant by virtual crossmatch? What are the pros and cons?
A virtual crossmatch (VXM) is used to ascertain the presence of HLA antibodies in a transplant recipient’s serum and to determine, virtu- ally, the potential flow cytometric crossmatch (FXM) results with an available donor.
VXM testing is routinely used to aid in the selection of donor kidneys for highly sensitized patients. A VXM can be a valuable tool in helping to minimize cold ischemia time and therefore improve donor organ allocation.
The correlation of the virtual crossmatch with flow cytometry crossmatch is greater than 85% . It requires HLA typing of the donor and a recent anti-HLA profile of the potential recipient. To ensure a correct anti-HLA profile at the time of the transplant call, regular collection of sera every 3 months is required for antibody screening via solid-phase assays, because antibody titres and specificities can change over time. Any potential sensitizing events like pregnancy, blood transfusions and previous transplantation must be documented accurately.
A false negative virtual crossmatch can arise from 1-Incomplete typing of the donor 2- donorspecific antibodies in the recipient serum against a unique HLA epitope which is not available on the SAB panel, can give rise to a false negative result
not all donor-specific antibodies detected by LuminexSAB are detrimental to graft outcomes. Studies have shown that donor-specific antibodies detected by SAB but with a negative CDC-XM are a major risk factor for early allograft rejection and long-term graft loss
False positives may result from 1-antibodies directed at HLA epitopes that come about secondary to denatured HLA antigens on the SAB 2-the presence of null alleles, which are not expressed as antigens on the cell surface in vivo
advantages the detection of acceptable and unacceptable antigens This avoids unnecessary shipping of organs resulting in less surgery delays, reduces cold ischaemia time, encourages cost savings and improved transplanting highly sensitized patients. A number of studies have reported low risk for early antibodymediated rejection and good allograft survival even in sensitized patients when using the virtual crossmatch
Disadvantage Denatured human leucocyte antigens on single antigen beads may lead to a false positive result Requires more coordination between immunology lab personnel and transplant team
Reference 1-Roberta Callus, Jesmar Buttigieg, Andrei Agius Anastasi, Ahmed Halawa, Basic concepts in kidney transplant immunology. British Journal of Hospital Medicine, January 2017, Vol 78, No 1.
1-What information do you need to know to support your decision? –ABO compatibility for recipient and donor. -HLA typing for recipient and donor (CDC , FCXM and cPRA). -Luminex-SAB (single antigen bead) did not identify any donor specific antibodies (DSA). -History of sensitization (blood transfusion-prior transplantation). –As serum or lymphoid tissue are not available to do physical crossmatch like CDC of flow cytometry,Virtual cross-match is possible application. 2-Will you accept this offer and go ahead with the transplantation?
-Yes; I will accept This Deceased Donner for transplantation;
-which is (Young age 34Y-with no past medical history and with excellent kidney function),
-which considered standard immunological risk for renal Transplantation (000 mismatch -No DSA). 3-What is meant by virtual crossmatch? What are the pros and cons?–In virtual crossmatch (VXM), both donor HLA typing and solid phase antibody screening are utilised together. It is not precisely a crossmatch in the sense of mixing serum and lymphocytes.
-The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
-This is particularly important in deceased donor renal transplantation. Quick results mean less cold ischemia times.
-The speed of results generated allows a VXM to be performed at the time of donor identification owing to the fact that there is progressively sensitive and specific flow cytometry technology.
-VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a prospective crossmatch strategy, and thereby, allows to consider a potentially positive crossmatch a risk factor for donor selection. -The VXM should, therefore, be done considering all available serum results including at least one recent within less than 3-6 month for a given patient.
-The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
–False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors.
– False negative results of VXM may arise due to the fact that the list of all potential HLA donor antigens have been classed differently and, therefore, can not be correctly represented.
-Furthermore, VXM does not identify the HLA “Null” alleles. Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
-In excess of 190 null alleles have been identified across HLA class I and II.
-There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation. -References; –Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339. -Gupta A, Iveson V, Varagunam M, Bodger S, Sinnott P, Thuraisingham RC. Pretransplant donor-specific antibodies in cytotoxic negative crossmatch kidney transplants: are they relevant? Transplantation. 2008;85:1200–1204. -Tinckam KJ. Basic histocompatibility testing methods. In: Chandraker A, editor. Core concepts in renal transplantation. New York: Springer Science + Business Media, LLC; 2012. pp. 21–42. -Gebel HM, Bray RA, Nickerson P. Pre-transplant assessment of donor-reactive, HLA-specific antibodies in renal transplantation: contraindication vs. risk. Am J Transplant. 2003;3:1488–1500. -Bray RA, Nolen JD, Larsen C, Pearson T, Newell KA, Kokko K, Guasch A, Tso P, Mendel JB, Gebel HM. Transplanting the highly sensitized patient: The emory algorithm. Am J Transplant. 2006;6:2307–2315.
What information do you need to know to support your decision?
*Blood grouping of both patient and recipient. *Allo antibodies testing against HLA (A, B,C,DRB1, DRB 3,4,5, DQB1, DQA1, DPB1, DPA1) plus other non-HLA antigens,., * Is the recipient have any history of potential sensitization . *Is the alloantibody testing sample is recent ?? according to the local program determination of the definition of a “recent” sample. * Is there any agreement between the laboratory and the transplant program which describe the circumstances when a prospective physical crossmatch is required. *Is the donor typing include HLA and other histocompatibility antigens to which antibodies have been identified in the potential recipient. * Virology screening of both donor and recipient and other required systemic evaluation of recipient and donor regarding preparation of kidney transplant .
Will you accept this offer and go ahead with the transplantation?
Yes if fulfill the criteria of virtual crossmatching that agreed by laboratory director or a technical supervisor who meet the clinical consultant qualifications and serve in this role.
What is meant by virtual crossmatch? What are the pros and cons
Virtual crossmatch (VXM)is an assessment of immunologic compatibility based on the patient’s alloantibody profile compared to the donor’s histocompatibility antigens. Based on well defined antigens and antibodies .Antibody presence or absence should be confirmed by more than one method and should be reconfirmed on an on-going basis ¬ Histocompatibility can be defined as encompassing both HLA and non-HLA components. For non sensitized patients who do not have circulating antibodies, PXM result against any prospective donor can be assumed to be negative ,although VXM is a risk assessment tool and there is currently no consensus on the goal of VXM— whether the risk assessment involves predicting the result of a PXM or the posttransplant outcome.
Prons of VXM:
Potential Benefits of Virtual Crossmatchesfor the patients,laboratory and transplant program : For patients : -It decrease the time needed for evaluation of compatibility (particularly with thoracic transplant patients); results in more efficient use of the system . ¬ Reduced cold ischemia time. ¬ Better matched donor/recipient by Increasing sensitivity and specificity of testing . ¬ Less likely to deny access for a false positive physical crossmatch . ¬ Facilitates matching over larger geographic areas, renal paired donations, and the transplantation of more highly sensitized patients by providing better access to sensitized patients . ¬ Reduced cost and waiting time . ¬ Performance of a physical XM is not precluded and can be completed concurrently with or after transplantation. ¬ It works as a risk assessment for patient desensitization needs. For the Laboratories: ¬ It allows better coordination and communication with transplant programs. ¬ Improvement of quality management with better patient and transplant program satisfaction. ¬ Increased efficiency, which allows for more focus on patients with problems and results in cost savings. ¬ It helps in decreasing on-call time expenditure by testing personnel. For the transplant programs: ¬ Reduction of ischemia time . ¬ Improvement of risk assessment for rejection ¬ Improved transplant physician and patient satisfaction by improving access to transplantation for geographically and immunologically disadvantaged candidates . ¬ Reduction of unexpectedly positive physical crossmatches which leads to more efficient use of transplant personnel. ¬ Optimization of immunosuppression and desensitization protocols ¬ Management of transplant related logistics (i.e. OR schedules) will be more flexible . Cons :
Potential Disadvantages of Virtual Crossmatches for patients laboratory and transplant program : For patients : ¬ There is potential to deny use of a donor organ that could be successfully transplanted . ¬ Requires patient to receive and understand more complicated information ¬ Negative crossmatch (physical or virtual) does not guarantee compatibility.
For the laboratories : ¬ Potentially more difficult for staff to maintain competency in performing physical crossmatches when they are done less frequently . ¬ Increased unreimbursed interpretation time. ¬ Requires more coordination with the transplant program. For transplant programs: ¬ Program staff have to learn a new interpretive vocabulary. ¬ Additional time and work to ensure that patients understand their risk and get all the information on time . ¬ No reimbursement for time/effort of professional rendering a virtual crossmatch. Reference: 1.https://www.cdc.gov/cliac/docs/addenda/cliac1114/8_BRAY_Virtual_Crossmatch_Workgroup_Report_Nov-2014.pdf 2.Principles of Virtual Crossmatch Testing for Kidney Transplantation Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani Muthukumar4,5 3. Pinelli DF, Tambur AR. Virtual crossmatching for deceased donor transplantation: one size does not fit all. Kidney Int.2020;97:659–662. https://doi.org/10.1016/j.kint.2020.02.001
In the current scenario of full HLA match at HLA-A,B and DR without DSA:I will need for ABO compatibility and virtual cross match to proceed for transplantation.
Will you accept this offer and go ahead with the transplantation? If there is no ABO incompatibility and negative VXM ,I will proceed directly for transplantation. In the same time according to information available with full HLA match and no DSA ,we can proceed even without VXM.
What is meant by virtual crossmatch? What are the pros and cons?
Generally speaking ,The main target for cross match techniques is to identify the recipients who have anti HLA antibodies against a specific donor (Donor specific antibodies) and they have a higher chance for hyperacute rejection as result of the presence preformed antibodies. DSAs are commonly generated by previous transplantation, frequent blood transfusion and pregnancy.
The virtual crossmatch: The Wait Is Over
The Physical crossmatching is costly and time consuming.
This technique is based on the comparison between donor and recipients without requiring viable donor cells, depending on complete HLA typing of the donor and anti-HLA antibodies of the recipient. The use of the virtual crossmatch as a final decision to proceed with transplant across transplant centres can lead to decreased cold ischemia time and lower DGF rates without increased risk of rejection. These cross match results must be updated every 3 months especially in patients on cadaveric transplant list.
Titres, specificities, and presence or absence of antibodies could be changed by time.So the use of antibody specificity from historical serum sample (older than 6 months) could not predict a crossmatch with certainty. As well as Other factors that can influence antibody specificities should be considered, which include pregnancies, transplants and blood transfusions.
Cons of VXM: -False positive results of VXM when there is significantly low titre and/or non-complement binding antibodies,that can leads to wrong exclusion of potential donors. -False negative results of VXM due to the fact that the list of all potential HLA donor antigens have been classed differently and can not be correctly represented. The results from VXM are not 100% accurate and current practice mandates a physical crossmatch be performed as well.
What information do you need to know to support your decision?
—————————————————————————————-
1-The ABO compatibility.
2-Hisory of ;
a-DM ,hypertension and renal disease .
b-Chronic or recent active infection .
c-malignancy
d- risk for transmissible disease (viral infection )
Will you accept this offer and go ahead with the transplantation?
—————————————————————————–
With 000 HlA mismatches ,excellent kidney function ,compatible blood group and absence of DSA ,I will accept this donor depending on the virtual cross match .
What is meant by virtual crossmatch? What are the pros and cons?
——————————————————————————————— Compare the recipient anti HLA Abs and the donor HLA profile .Detects acceptable and unacceptable Ag.
Advantages of virtual cross match ; ——————————————————- 1- The virtual crossmatch ensures timely allocation of organs and increases the chance of transplantation in highly sensitized individuals.
2- May be performed with stored sera therefore shortening cold ischaemia time.
3-Increased sensitivity.
Disadvantages of virtual cross match ; —————————————————— 1-Denatured human leucocyte antigens on single antigen beads may lead to a false positive result.
2-Requires more coordination between immunology lab personnel and transplant team. Reference ; ——————— 1-Basic concepts in kidney transplant immunologyBritish Journal of Hospital Medicine, January 2017, Vol 78, No 1Dr Roberta Callus, Dr Jesmar Buttigieg, ,Dr Andrei Agius Anastasi, Mr Ahmed Halawa.
Disadvantages of virtual cross match ;
————————————————–
3-are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
What information do you need to know to support your decision?
When a cadaveric organ is offered for transplant, certain information is required before proceeding with the transplant. It includes:
a) Blood group compatibility of the donor and recipient.
b) Human leukocyte antigen (HLA) mismatch using HLA typing of the donor and recipient.
c) Assessment for presence of donor specific antibodies (DSA) in the recipient using a solid phase assay like Luminex which should not be very old (preferably done in last 3 months).
d) Virological screening including human immunodeficiency virus (HIV), hepatitis B and Hepatitis C viral infection, cytomegalovirus (CMV), Epstein Barr virus (EBV)
e) Any history of active infections/ malignancy in the donor.
Will you accept this offer and go ahead with the transplantation?
Yes. This recipient-donor pair has a 000 mismatch, with no DSA. Assuming that the blood group compatibility has been checked prior to the offer, even in absence of a crossmatch, due to negative virtual cross match (000 mismatch and no DSA), the offer is acceptable.
What is meant by virtual crossmatch? What are the pros and cons?
A virtual crossmatch (VXM) involves matching a pair of recipient and donor utilizing the HLA typing of the donor and the presence of antibodies in the recipient serum, which is done using a solid phase assay on a historical serum of the patient (1). There is no physical mixing of recipient serum with the donor lymphocytes.
The pros of VXM include: Shorter time to transplantation and cold ischemia time (it can be done even at the time of organ retrieval itself), increase chances of finding crossmatch negative donors for sensitized patients (by matching prior to physical crossmatch itself) (2).
The cons of VXM include: The VXM depends on the anti-HLA antibodies in the recipient. If the solid phase assay results for the anti-HLA antibodies was done more than 3 months back, or if there is history of sensitization after the last solid phase assay, then VXM cannot be relied upon. Also, presence of non-complement binding antibodies, or low-titre antibodies may lead to a false positive VXM, preventing a transplant (3). A false negative VXM can be due to misclassification of donor HLA antigens. A VXM does not identify ‘null alleles’, which have DNA sequences identifiable on molecular typing but do not express HLA on cell surface (1). In such a scenario, donor null allele can be identified as a fully expressed product by the recipient, and DSA can develop in the recipient if the expressed antigen is not present in the recipient, leading to difficulties in future transplantation. Additionally, if the donor HLA type is not present in the solid phase assay testing kit, then the antibodies against those HLA antigens could have been missed, hence VXM cannot be used in such a scenario (3).
References:
Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348. doi: 10.5500/wjt.v7.i6.339. PMID: 29312863; PMCID: PMC5743871.
Morris AB, Sullivan HC, Krummey SM, Gebel HM, Bray RA. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era. HLA. 2019 Dec;94(6):471-481. doi: 10.1111/tan.13693. Epub 2019 Oct 17. PMID: 31515937; PMCID: PMC7341023.
Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
What information do you need to know What is meant by
virtual crossmatch? What are the pros and cons?to support your decision?
We need to know
*Blood group of both donor and recipient
*HLA typing .
*past medical history of the donor.
*cause of kidney disease if the recipient.
*history of sensitization, Blood transfusion, pregnancy, previous transplant.
*Virology and chronic infections as CMV, EBV, Hbv ,HIV and TB.
* as there are no blood or lymph samples are available Virtual cross matching must be done recent before transplantation.
Will you accept this offer and go ahead with the
transplantation?
This is a good offer as there is no DSA and there is 000 mismatch, in absence of any other contraindications from history i will accept this donor
What is meant by virtual crossmatch? What are
the pros and cons?
American Society for Histocompatibility and
Immunogenetics defines VXM test as an assessment of immunologic compatibility
based on patient’s alloantibody profile compared with donor’s
histo-compatibility antigens.
The VXM
test uses the results of 2 independently done physical laboratory tests and
does not involve mixing of serum and cells.
Several transplant centres have reported their success with proceeding to transplant
based on VXM results and eliminating pre transplant PXM to reduce cold ischemia time in deceased kidney
donors.
The goal of VXM is pre transplant risk stratification— though there is no consensus on
whether such risk assessment involves predicting the PXM result or the post transplant
outcome.
Pros:
-Reduce cold ischemia time in deceased kidney donors
-Detect the unacceptable antigens
-VXM is more sensitive than PXM.
Cons:
– False positive results of VXM by detection of insignificant Ab
– Also detection of non-complement
binding AB that may miss a good offer and increase waiting time.
Technical issues related to the assay and a low threshold for calling an antibody as
present (over-calling) could result in a false-positive DSA result.
False negative results also may present as MFI cutoff values are different between labs.
-SAB manufacturing issues result in lot-to-lot
variability
-SAB assay use synthetic HLA on beads as the target and may not reflect the cellular profile—for example, cell
surface expression of HLA-C is lower than HLA-A and -B, but this is not reflected on the beads.
Reference:
Madhu C.
Bhaskaran, Sebastiaan Heidt.Principles of Virtual Crossmatch Testing for Kidney
Transplantation .kidney Int Rep (2022) 7, 1179–1188.
What information do you need to know to support your decision?
I will need the following information:
* For both the donor and the recipient: Blood group, HLA typing with virtual cross match, viral serology including CMV and EBV.
* For the recipient I need to know the primary cause of renal failure, sensitization history which includes history of previous transplant, pregnancy or blood transfusion and previous DSA tests and when the patient had last SAB test ?
* For the donor, I need to know the warm ischemia time, type of deceased donor (DCD vs. DBD)
Will you accept this offer and go ahead with the transplantation?
I will accept this offer with 000 mismatch and no DSA, excellent graft function for previously healthy young donor.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch (VXM) assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing. The goal is only for pretransplant risk stratification and there is no consensus that will predict the result of physical crossmatch PXM or the outcome of the transplantation.
The pros of VXM includes increased sensitivity, can be performed in shorter time and decrease the cold ischemia time, improve access to the transplantation for highly sensitized patients and can improve this risk assessment for graft rejection.
The cons of VXM includes the false positive results which can occur due to denatured HLA or SAB. The usage of historical serum sample in VXM can result in false negative test as presence of antibodies can vary significantly overtime. VXM requires more coordination between immunology lab and personnel and transplant team. For that, the results of VXM are not always accurate and PXM is still mandatory in most cases.
· ABO blood group · Recent HLA antibody testing of recipients (3-6 m) · complete HLA typing of donor
· History of previous sensitization (pregnancies, transplants and blood transfusions.) · Infectious risk for (CMV/EBV) If virtual cross match negative for class I/II I can proceed
Virtual crossmatch both donor HLA typing and solid phase antibody screening are used together. by “mixing” identified antibody specificities of recipient serum with donor HLA antigens
Pros
· shorter wait times
· improving organ allocation system
· less costs
· shorter cold ischemia time
· rapid result
· facilitating kidney paired donation programs
· we can consider donors that would not be available by means of physical crossmatch strategy,
cons
presence or absence of antibodies changes over time. so we should consider all available serum including at least one recent within less than 6 month
False positive results IF the titre is low or in the presence of non-complement binding antibodies,
false negative as all potential HLA donor antigens may not be correctly represented.
virtual cross match does not identify the HLA “Null” alleles.
so The results from VXM are not a hundred percent accurate
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing.
The goal of VXM is pretransplant risk stratification, though there is no consensus on whether such risk assessment involves predicting the PXM result or the posttransplant outcome.
VXM-based approach has resulted in a statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes.
What are the pros and cons?
The pros and cons of something are its advantages and disadvantages, which you consider carefully so that you can make a sensible decision.
The pros:-
Less time needed for evaluation of compatibility (particularly with thoracic transplant patients); results in more efficient use of the system.
Reduced cold ischemia time.
Facilitates matching over larger geographic area, renal paired donations, and the transplantation of more highly sensitized patients.
Can result in improved access for sensitized patients
Increased sensitivity and specificity of testing can lead to a better matched donor/recipient.
More specific than serologic crossmatch-(includes patient history, etc).
Less likely to deny access for a false positive physical crossmatch.
Reduced cost.
Does not preclude the performance of a physical XM; however, this may be completed concurrent with or after transplantation.
Aids in risk assessment for patient desensitization needs.
Potential Benefits-cont’d
Laboratories?
Increased efficiency, which allows for more focus on patients with problems and results in cost savings.
Decreased on-call time expenditure by testing personnel.
Allows for better coordination and communication with transplant programs.
Improved quality management with better patient and transplant program satisfaction.
Transplant programs?
Reduced ischemia time.
Improved access to transplantation for immunologically and geographically disadvantaged candidates, which results in improved transplant physician and patient satisfaction.
Fewer unexpectedly positive physical crossmatches leads to more efficient use of transplant personnel.
Improved risk assessment for rejection.
Allows for optimized immunosuppression and desensitization protocols.
Flexibility in managing transplant related logistics (i.e. OR schedules).
Cost savings
Others?
Benefits donor families in that there is a greater possibility that donated organs will be used.
Cost savings to payers.
The cons:-
Based on the program’s criteria for crossmatches, there is potential to deny use of a donor organ that could be successfully transplanted.
Requires patient to receive and understand more complicated information.
Negative crossmatch (physical or virtual) does not guarantee compatibility
laboratories?
Potentially more difficult for staff to maintain competency in performing physical crossmatches when they are done less frequently.
Increased unreimbursed interpretation time.
Requires more coordination with transplant program.
transplant programs?
Program staff have to learn a new interpretive vocabulary
Additional time and work to ensure that patients understand their risk and get all the information on time.
others?
No reimbursement for time/effort of professional rendering a virtual crossmatch
Bray R.A. The acceptability and application of virtual crossmatching in lieu of serologic crossmatching for transplantation. Virtual Crossmatch Work Group Report. Centers for Disease Control and Prevention.(Published 2014. Accessed April 1, 2022.).
What information do you need to know to support your decision?
more information about the cross match between donor and recipient
more detailed history about the recipient ,especially about previous sensitizations
Will you accept this offer and go ahead with the transplantation?
yes, after an MDT discussion we willaccept as a good candidate with zero cross match and no DSA.
What is meant by virtual crossmatch? What are the pros and cons?
virtual cross match is a rapid computerized cross-match among the pools of donors to identifying a high risk or sensitized recipients
PROS:
allow you a short time to access the kidney and shorten waiting time
CONS:
lesser reliable test in compared to some other types of cross-match studies
This is a good donor with 000 mismatch and no DSAs
The important information required here is:
Potential donors blood group
Any past history of malignancy, chronic infections
Social history – to determine if he is high risk for any transmissible diseases like HIV, Hepatitis B or C
Family h/o DM, HTN, kidney disease, malignancy
During retrieval of the organs, the surgical team need to asses the thoracic cavity and abdominal cavity for any lymph nodes, tumors, features of TB on the peritoneum
Since no blood is available for crossmatch, we can do a virtual crossmatch
Would you accept to this donor?
Yes I would accept this donor and proceed with the transplant
Virtual crossmatch:
The virtual crossmatch refers to a process where the actual results of the recipient HLA Ab are compared to the donor HLA Ag to determine what the actual crossmatch results would be
The virtual crossmatch has a positive predictive value of > 85% but a low negative predictive value of 50% . This is because of the incomplete profile of the recipients HLA Ab
What information do you need to know to support your decision?We still need to know donor and recipient blood group. The other question should aim to go through the donor’s medical history, in particular history of infections or malignancy. Recipient history of sensitization events should be taken in consideration including blood transfusion, pregnancy, previous transplantation.
Will you accept this offer and go ahead with the transplantation?Yes I will accept the kidney offer after making sure that blood group is compatible and no risk of infection transmission.
What is meant by virtual crossmatch? What are the pros and cons?The need for a final “physical” crossmatch has been significantly reduced thanks to the “virtual” crossmatch, which matches the patient’s antibody profile to the donor’s HLA type. It is mostly utilized in kidney transplants from deceased donors.
Cons
Any source of sensitization, including pregnancy, blood transfusions, and previous transplants might impact virtual crossmatch.
Pros
It matches FCM cross match
Define inappropriate antigens to reject donors.
What information do you need to know to support your decision?
-ABO blood grouping
-HLA typing for HLA A ,B ,DR
It will be needed in this deceased donor to save time and reduce cold ischemia time
-HLA crossmatching(VXC) requiring HLA typing and solid phase screening
-DSA recent test
-CPRA
-Virological screening
-History of sensitisation need to be excluded as blood transfusion ,pregnancies as well as ,previous infections ,malignancies ,DBD or DCD Will you accept this offer and go ahead with the transplantation?
Yes, since there is 000 mismatch and no DSA ,therefore seems to be of standard immunological risk transplant. What is meant by virtual crossmatch? What are the pros and cons?
Virtual cross match uses donor HLA typing and solid phase antibody screening in vitro to crossmatch results by mixing the recipient’s serum harbouring specific Ab with donor HLA antigens . Pros
It can shorten waiting times and improve sensitised transplants outcomes .It can be carried out at the time of donor identification because of the presence of progressively sensitive and specific flow cytometry technology enabling consideration of potentially positive crossmatch which is a risk factor for donor selection therefore saving grafts. Cons
Old serum sample with specific antibodies are used rendering crossmatch prediction not precise enough also other factors can affect the antibody specificities therefore a recent serum sample must be available within less than 3 -6 months time range.
False positive results can occur with very low Ab titre and/or non-complement binding antibodies
False negative results because all potential HLA donor antigens are classed differently and are not correctly represented
It does not identify the HLA “Null” alleles which have lower risk in SOT but can affect future transplants. Reference
-Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017 December 24; 7(6): 276-363
What information do you need to know to support your decision? Ø Blood group for donor and recipient Ø Cross match Ø DSA Ø Virology screen HBV,HCV,HIV and CMV Ø Regarding the recipient we need to know any history of previous abortion ,miss carriage previous transplant and recent blood transfusion . History diabetes or hypertension . Will you accept this offer and go ahead with the transplantation? Ø Yes. zero mismatch ,no DSA What is meant by virtual cross match? What are the pros and cons?
Ø Virtual cross match: VXM It is test assess immunologic compatibility between recipient and donor by analyzing result of 2 independently done physical laboratory tests –patient anti HLA antibody and donor HLA typing .
Advantage 1 increased sensitivity 2-improves risk assessment for rejection 3- improves transplantation access for highly sensitized patient 4- may be performed with stored sera there for shortening cold ischemia time . Disadvantage : 1- Required more coordination between immunology lab personal and transplant team 2- Beads may lead to false positive result
What information do you need to know to support your decision?
– ABO compatibility.
– HLA compatibility
– Virology screening CMV, EBV, HIV.
– History of any sensitizing events for both donor and recipient.
– Recent cPRA
– Recent updated anti-HLA antibodies profile for the recipient.
– Virtual cross matching.
Will you accept this offer and go ahead with the transplantation?
Providing the absence of new sensitizing event and virtual cross match was negative. Yes, this donor can be accepted as is a good match and no DSA.
What is meant by virtual crossmatch? What are the pros and cons?
– VXM is a risk assessment tool, determine the immunologic compatibility between a recipient and a donor by analyzing and comparing the results of 2 independently done laboratory tests—patient anti-HLA antibody and donor HLA typing.
-A virtual crossmatch can predict actual crossmatch results based on antibody specificity and strength detected by solid-phase assays.
-Accurate prediction relies heavily on up-to-date HLA antibody testing of recipients and complete HLA typing of donors. Pros: – Significantly improved organ allocation efficiency.
– Define unacceptable antigens
– Reduced testing costs.
– Shorter wait times and cold ischemia time
– VXM is potentially more sensitive than PXM to detect the presence of DSA.
– Does not require a viable cell.
– Enables transplant surgeons to examine donor organs that would not otherwise be accessible using a prospective crossmatch technique, making a possibly positive crossmatch a risk factor for donor selection.
Cons: – The use of antibody specificity from historical sample (earlier than 6 months) could not predict a crossmatch with certainty. –False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies or denatured human leukocyte antigen on SAB.
– The result varies according to the laboratory’s MFI cutoff values
– False negative results due to:
– The fact that the list of all potential HLA donor antigen, cannot be correctly represented.
– HLA structure present on the SAB assays differs between the 2 vendors that are currently available
– Shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen
– Inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect).
– VXM does not identify the HLA “Null” alleles. Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
References:
-Human leukocyte antigen typing and crossmatch: A comprehensive review Mohammed Mahdi Althaf, Mohsen El Kossi, Jon Kim Jin, Ajay Sharma, Ahmed Mostafa Halawa World J Transplant 2017 December 24; 7(6): 276-363
-Principles of Virtual Crossmatch Testing for Kidney Transplantation Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani Muthukumar Kidney Int Rep (2022) 7, 1179–1188
What information do you need to know to support your decision?
· ABO compatibility
· HLA matching (here 000 mismatch)
· Donor condition: infection, malignancy, DCD or DBD, and others
· Recent DSA
· History of sensitization (blood transfusion, abortion, and previous transplant)
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept in case of this best HLA match, no DSA, and –ve virtual crossmatch
What is meant by virtual crossmatch? What are the pros and cons
*The ELISA, flow cytometry or Luminex assay is run against a fixed panel of HLA antigens from past organ donors in a large computerized database and the percentage of specific unsuitable antigens reported
*This “virtual cross-match” is called as calculated PRA (cPRA) in the US and calculated Reaction Frequency (cRF) in UK
*PRA/cPRA measures the level of HLA sensitization, the recipients’ likelihood of a positive
cross-match but cannot determine the presence of antibodies against a certain donor kidney
Pros:
1. Quick (shorter wait times)
2. Tests against a large number of fixed and consistent HLA antigens
3. Can be performed at the time of donor identification
4. Consider a potentially positive crossmatch depending on a risk factor for donor selection
Cons:
1. The use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty
2. False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies
3. False negative results due to the fact that the list of all potential HLA donor antigens have been classed differently
4. The results from are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well
5. Does not identify the HLA “Null” alleles (are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface)
References
1. Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348. doi: 10.5500/wjt.v7.i6.339. PMID: 29312863; PMCID: PMC5743871.
2. Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
3. Mohanka R, E Kosi M, Jin J, Sharma A, Halawa A. Careful Interpretation of HLA Typing and Cross-Match Tests in Kidney
Transplant. JOJ uro & nephron. 2017; 3(5): 555625. DOI:
Thankyou but you need to revise some facts:
the antigens are on the lymphocytes so what you need from the donor (deceased) is a lymph node or a punch from the spleen but not kidney.
VXM is between donor ANTIGENS and recipient DSAs ( antibodies)
Other needed information
1- History : Patient gender and ethenicity ,presence of any chronic medical illness as diabetes or HPN or any infectious diseases specially HIV . HBV and HCV or malignancy.
2- Cause of death, utilization of positive inotropes , UOP ,presence of end organ damage , his last lab including KFT
3- ABO and results of virtual cross match Will you accept this donor
Yes, I will accept his if no absolute contraindication was found as no active malignanacy or infection . From immunological point of view this is a suitable donor as 000 mismatch and no DSA . Virtual cross match
Used to assess immunological compatibility between donor and recipient and to detect the presence of preformed DSA through comparing the results of tissue typing of both donor and recipient that were perfomed separarely .It’s virtual as it doesn’t include actual physical tissue examination and it helps to shorten cold ischemia time ,but it does not predict the results of physical cross match , so it is better to preserve VXM for low risk ,non sensitized patient . Pros of VXM:
1- Shorten cold ischemia time .
2- Comparable results with physical cross match specially in non sensitized recipients
3- Lower cost and better results in detecting both serological and epitop DSA
Cons of VXM:
1- Some alleles are missed in LSAB kits as LSAB contains only 100 allele for each HLA class , so require specific kits to test for these alleles .
2- False results may occur from denatured protients on LSAB beads.
3- Cannot detect presence or effect of inhibitory mediators in recipient serum .
4- Requires coordination between labs as there is variation in SAB beads according to manufacrurer
Ref:
1- Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi
2- Peng B, Zhuang Q, Yu M, Li J, Liu Y, Zhu L, Ming Y. Comparison of Physical Crossmatch and Virtual Crossmatch to Identify Preexisting Donor-Specific Human Leukocyte Antigen (HLA) Antibodies and Outcome Following Kidney Transplantation. Med Sci Monit. 2019 Feb 3;25:952-961
1) What information do you need to know to support your decision?
Blood grouping, history of sensitization (pregnancies, previous transplants and blood transfusions).
2)Will you accept this offer and go ahead with the transplantation?
Yes. I will accept this donor with 0,0,0 HLA mismatch, which is good and negative DSA because renal transplantation remains the best option for patients with (ESRD) than dialysis.
3) What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatching (VXM):
In (VXM), both donor HLA typing and solid phase antibody screening are employ together.
It is not absolutely a crossmatch in the sense of mixing serum and lymphocytes.
The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
It is helps in cases when a prospective crossmatch strategy not available, and thereby, allows to consider a potentially positive crossmatch a risk factor for donor selection
Titres, specificities, and presence or absence of antibodies could significantly vary over time. Thus, the use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty. Other factors that can influence antibody specificities should be considered, and these include pregnancies, transplants and blood transfusions.
The VXM should, therefore, be done considering all available serum results including at least one recent within less than 3-6 mo for a given patient. False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors. The VXM can also give false negative results due to the fact that the list of all potential HLA donor antigens have been classed differently and, therefore, can not be correctly represented. The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well. Furthermore, VXM does not identify the HLA “Null” alleles. Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. In excess of 190 null alleles have been identified across HLA class I and II. There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation. A recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product and, therefore, transplanted with a donor bearing the expressed antigen. This mismatch is not life threatening but can affect future transplantation. In contrast, where a donor null allele is misidentified as a fully expressed product and subsequently transplanted into a recipient bearing the expressed antigen results in no humoral rejection and is well tolerated.
Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017; 7(6): 339-348 [PMID: 29312863 DOI: 10.5500/wjt.v7.i6.339]
Dear All Thank you for your reply I agree with the virtual crossmatch, but what criteria are required to perform a VXM in the index case? What is “HLA null allele” meant and how would they affect the results of VXM?
You have missed an essential requirement that is needed to perform a VXM.
What criteria are required to perform a VXM in the index case? Rapid crossmatching in sensitized recipients, from a cadaveric Donor, shown to improve outcomes in sensitized recipient. Identify best donor in short time.
What is “HLA null allele” meant and how would they affect the results of VXM? Null HLA alleles have identifiable DNA sequences with molecular typing, but do not express HLA products on the cell surface. Thus; the recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product, which may result in no no humeral rejection that is tolerable.
Thank you Dr Hassan for the HLA null allele but Have you read the question carefully about what criteria are required to perform a VXM in the index case?
When using VXM, we rely on donor HLA typing, so if null allele is misidentified as fully expressed antigen, this may change the decision due to finding of DSA in the recipient, that would be not significant
HLA alleles that have identifiable DNA sequences with molecular typing but with no cell surface antigen expression. These alleles termed “null” HLA alleles are of less immunological significance
VXM offers shorter waiting time, better with deceased donation, provide more donors who were not accepted before by conventional CM, so it can be better in highly sensitized patient
Do you think null” HLA alleles ‘are of less immunological significance’? Are you aware that your VXM result will be reliant on donor antigens which are actually ‘in real life’ are not expressed on the donor cell surface, they are only detected on the level of DNA sequencing?
Identification of the donor, solid phase antibody screening, donor typing
HLA null alleles; are the ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. In excess of 190 null alleles have been identified across HLA class I & II . There is a significant risk where null allele is misidentified for its fully expressed counterpart in stem cell transplantation. How ever the risk is slightly low in solid organ transplantation. A recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully express product and therefore, transplanted with donor bearing the express antigen. VXM does not identify the HLA null alleles.(Mohammed Mahdi Althaf at. el)
Thank you Dr Lomatayo You referred to ‘Identification of the donor, solid phase antibody screening, donor typing’ asessential requirement that is needed to perform a VXM? Do you think these are the essential requirement to perform VXM?
– Donor HLA typing and solid phase antibody screening are needed to perform VXM
-Null HLA alleles are HLA alleles with identifiable DNA sequences with molecular
typing but with no cell surface antigen expression. The null HLA alleles are of less immunological significance
What is “HLA null allele” meant and how would they affect the results of VXM?
HLA null alleles are characterized by the lack of a serologically detectable product.
Because serological HLA diagnostics are increasingly replaced by DNA-based typing methods considering only small regions of the genes, null alleles may be misdiagnosed as normally expressed variants.
Failure to identify them as non-expressed variants may result in an HLA mismatch that is highly likely to stimulate allogeneic T cells.
Luis Alberto Marin Rubio, Jose Daniel Aroca‐Aguilar, Mar Luis‐Hidalgo, Julio Escribano, Jesus Ontañon, RNA and protein expression analysis of allele: A null allele renamed as , HLA, 10.1111/tan.14537, 99, 3, (160-166), (2022)
==================================================================== I agree with the virtual crossmatch, but what criteria are required to perform a VXM in the index case?
It has been demonstrated that quick crossmatching from a cadaveric donor improves outcomes in sensitized recipients and quickly identify the ideal donor.
Virtual crossmatch (VXM) combines donor HLA typing and solid phase antibody screening to forecast in vitro crossmatch results, leading to shorter wait times and improved outcomes for sensitised transplant recipients.
What is “HLA null allele” meant and how would they affect the results of VXM?
HLA null allele are alleles that have no HLA products on the cell surface but have identifiable DNA sequence detected by molecular typing, it is non-immunogenic
More than 190 null alleles are identified in both class I and II HLA
IF the recipient null allele is misidentified as fully expressed product (by molecular typing), there is a risk of choosing a donor with the same expressed antigen, leading to the development of DSA in the recipient against that antigen after transplantation.
Although this mismatch is not fatal but it may increase the risk of rejection and affect graft survival
On the other hand, if donor null allele is misidentified as fully expressed product, and transplanted to a recipient with the same expressed antigen, at that time no DSA will develop since null alleles are not immunogenic
This condition is more significant in stem cell transplantation than solid organ transplantation
Serological typing can identify null alleles, and may avoid this problem
This condition is importent when using VXM, since we rely on donor HLA typing, so if null allele is misidentified as fully expressed antigen this may change the decision due to finding of DSA in the recipient through luminex which is not clinically significant
You have missed an essential requirement that is needed to perform a VXM.
VXM is done in deceased donor transplantation, in order to perform VXM we need to have donor HLA typing and recipient solid phase assays (ELISA or beed assay- luminex)
DSA may change over time due to sensitization from blood transfusion or pregnancy so luminex SAB should be repeated every 3 m.
Wet cross match should be performed in only sensitized patients as there may be a new DSA that develop, this should be detected by wet cross match (positive FCXM, negative VXM), in non-sensitized recipient we can rely on VXM in proceeding in transplantation
“null” HLA alleles :
The ability to differentiate HLA alleles that have identifiable DNA sequences with molecular typing but with no cell surface antigen expression. These alleles termed “null” HLA alleles are of less immunological significance
Criteria are required to perform VXM:
· To assess alloantibody
· For patient with no identified alloantibody
· Recipient with history of blood transfusion ,previous transplant ,pregnancy (female ).
We do VXM for cadaveric renal transplant, Donor HLA typing and recent recipient SAB are required.
Null HLA alleles has no cell surface antigen expression ir serologically detectable produces although there is identifiable DNA sequences with molecular
typing. There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation but this risk is lower in solid organ transplantation. The risk occur mostly when the recipient null allele is misidentified as fully expressed product as this will lead to the development of DSA in the recipient against that antigen after transplantation which is still not life threating but can affect future transplant.
what criteria are required to perform a VXM in the index
case?
VXM is required in deceased kidney donors for rapid matching
and shorter cold ischemia time .
To perform VXM both donor HLA typing and solid phase antibody screening are utilised together.
Titres, specificities, and presence or absence of antibodies could significantly vary over time so the results must be recent within 3 months
taking into consideration recent sensitization events .
What is “HLA null allele” meant and how would they affect
the results of VXM?
Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
In excess of 190 null alleles have been identified across HLA class I and II.
There is a significant risk where a null allele is
misidentified for its fully expressed counterpart in stem cell transplantation.
However, the risk is slightly lower in solid organ transplantation.
A recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product
and, therefore, transplanted with a donor bearing the expressed antigen.
This mismatch is not
life threatening but can affect future transplantation.
The risk of missing null allele is high in VXM, as donor HLA typing may not detect this null allele due to lack of cell surface product, and its not expressed as antigen.
And we can’t determine the donor’s DSA against this allele which will affect the graft if present
what criteria are required to perform a VXM in the index case?
A VXM is a tool to reduce cold ischemia time in cadaveric transplantation
To perform a VXM, 2 things are essential:
1) HLA typing of the donor
2) Solid phase assay/ Single antigen bead (Luminex) test of the recipient to detect anti-HLA antibodies in the recipient. The test should be as recent as possible (not more than 3 months old), and a sensitizing event like blood transfusion/ pregnancy etc should not have occurred after the last single antigen bead test.
What is “HLA null allele” meant and how would they affect the results of VXM?
A VXM does not identify ‘null alleles’, which have DNA sequences identifiable on molecular typing but do not express HLA on cell surface. In such a scenario, donor null allele can be identified as a fully expressed product by the recipient, and DSA can develop in the recipient if the expressed antigen is not present in the recipient, leading to difficulties in future transplantation. It will have no effect if the recipient expresses the antigen.
Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. In excess of 190 null alleles have been identified across HLA class I and II.
There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation.
For a virtual crossmatch to be allowed the results for the recipient need to be less than six months old. Factors like pregnancy and blood transfusion need to be taken into account as well
One of the key requirements of a virtual crossmatch is that a physical crossmatch has to take place which in this case will not be possible.
The virtual crossmatch also does not take into account the null alleles
HLA null alleles refers to the genetic mutations that code for non-functional proteins or proteins that are not expressed on the cell surface. Null alleles produce no serologically identifiable products. These can cause problems in transplantation especially for HSCT and less so for SOT
-The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
-This is particularly important in deceased donor renal transplantation. Quick results mean less cold ischemia times. -Null HLA alleles; are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
-In excess of 190 null alleles have been identified across HLA class I and II.
-There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation.
HLA null alle DNA sequence with molecular typing but no cell surface antigen expression and less immunogenic significance.
VXM is need donor HLA typing and recipient solid phase assay
the risk of null alleles is misleading for its fully expressed in stem transplantation, however, the risk is lower in solid organ transplantation which leads to DSA formation but has no life threaten effect. References Patel R, Terasaki PI. Significance of the positive crossmatch test in kidney transplantation. N Engl J Med. 1969;280(14):735–739. [PubMed] [Google Scholar]
What criteria are required to perform a VXM in the index case?
The VXM involves matching of HLA typing of the donor and the presence of antibodies in the recipient serum, which is done by using a solid phase assay on a historical serum of the patient .There is no physical mixing of recipient serum with the donor lymphocytes.
V XM more sensitive than Actual XM
To perform a VXM we need:
1) HLA typing of the donor
2) SAB (Luminex) test to detect anti-HLA antibodies in the recipient, For last three month and a sensitizing event like blood transfusion/ pregnancy etc should not have occurred after the last recent single antigen bead test.
What is “HLA null allele” meant and how would they affect the results of VXM? HLA null allele DNA sequence with molecular typing but no cell surface antigen expression and less immunogenic significance. VXM is need donor HLA typing and recipient solid phase assay the risk of null alleles is misleading for its fully expressed in stem transplantation, however, the risk is lower in solid organ transplantation which leads to DSA formation but has no life threaten effect.
-Not all alleles represented on beads (too many )
-Not all proteins currently type for use historical serum => patient have entire immune history before listing cannot predict what you have never tested and cannot assess for potential immune memory
the result of the recipient’s solid-phase antibody screening
VXM method helps to shorten waiting time and could lead to an improved outcome in the sensitized recipient.
HLA null allele
These are alleles that have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. They are of less immunological significance and can not be detected by VXM.
The virtual crossmatch requirements: · the VXM does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient. · The prerequisite to benefit from the advantages of just VXM testing is the determination of unacceptable antigens by SAB assay and to predict the actual PXM results.
The null HLA: · HLA null alleles: code HLA antigens with low or no cell surface expression. · Null alleles are not detectable by standard serological typing methods and may be overlooked/or incorrectly assigned by available DNA methods. · The failure to identify an HLA null allele as a non-expressed variant in the stem cell transplantation setting may result in an HLA mismatch that is highly likely to stimulate allogeneic T cells and to trigger graft-vs-host disease. · The prevalence of HLA null alleles may be around 0.3% or even higher(1). · For some HLA null alleles, the translation into a truncated polypeptide chain seems possible, which thus might act as minor histocompatibility antigens. · Complete sequence of exons 2 and 3 for class I and exon 2 for class II molecules by sequencing-based typing was deemed the best technique in reducing problems with ambiguities and null alleles(1)
References 1. Elsner HA, Blasczyk R. Immunogenetics of HLA null alleles: implications for blood stem cell transplantation. Tissue Antigens. 2004 Dec;64(6):687-95. doi: 10.1111/j.1399-0039.2004.00322.x. Erratum in: Tissue Antigens. 2006 Aug;68(2):191. PMID: 15546342. 2. Oudshoorn M, Horn PA, Tilanus M, Yu N.Typing of potential and selected donors for transplant: methodology and resolution Tissue Antigens. 2007 Apr;69 Suppl 1:10-2. doi: 10.1111/j.1399-0039.2006.758_5.x.PMID: 17445154
-The donor HLA typing and solid phase antibody screening are used simultaneously.
-HLA null alleles despite not expressing HLA products on the surface have similar DNA sequencing on molecular typing and thus may either show a false positive in some instances from the list of donor HLA donor antigens classed differently and misinterpreted or low titers of complement binding antibodies on the other hand may lead to false positives.
what criteria are required to perform a VXM in the index case?
Consider a virtual crossmatch when there are sufficient data on a patient’s alloantibody status to meet the transplant program- specific criteria. Also require donor typing to include HLA & other histocompatibility antigens to which antibodies have been identified in the recipient.
2. the result of the recipient’s solid-phase antibody screening.
VXM method helps to shorten waiting time and could lead to an improved outcome in the sensitized recipient.
HLA null allele:
These are alleles that have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. They are of less immunological significance and can not be detected by VXM.
Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. In excess of 190 null alleles have been identified across HLA class I and II.
There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation.
A recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product and, therefore, transplanted with a donor bearing the expressed antigen. This mismatch is not life threatening but can affect future transplantation.
In contrast, where a donor null allele is misidentified as a fully expressed product and subsequently transplanted into a recipient bearing the expressed antigen results in no humoral rejection and is well tolerated.
Thank you for your reply I agree with the virtual crossmatch, but what are the criteria required to perform a VXM in the index case? You have missed an important and essential requirement that is needed to perform a VXM.
2- yes will accept based on ABO and no DSA and 000 mismatch
3-virtual cross match is to compare HLA typing of the patient with donor, and consider antiHLA antibodies to the donor in the recipient, without doing wet cross match between the serum of the patient and lymphocyte of the donor
pros it is web based program , time saving, can be used in highly sensitized patient without paying attention to cPRA , can predict physical cross match and can replace it
the process is easy after introduction and usage of SAB technique, it is accurate and faster than physical CM, it can sort the patients depends on HLA matching, and CPRA.
cons still has time to review HLA of the patient and donor and detect unacceptable genes
Thank you for your reply I agree with the virtual crossmatch, but what are the criteria required to perform a VXM in the index case? You have missed an important and essential requirement that is needed to perform a VXM.
What information do you need to know to support your decision?
1. Check the proposed donor medical file, history of infections, medications, alcohol and sexual history, cardiac history, history of blood transfusion.. etc.
2. ABO compatibility, and cross match – lymphocytotoxicty, c-PRA , and DSA.
3. Type of donor death is it cardiac, or brain death, as DBD has better graft survival as well as less risk for delayed graft function.
4. CMV, EBV, and other viral screening for both donor and recipient.
5. The recipient cardiac status, screening for breath and cervical cancers, primary disease, smoking history. Will you accept this offer and go ahead with the transplantation?
Yes; I’ll accept this kidney for transplantation, however the is 000 mismatch which gave and excellent prognosis.
What is meant by virtual crosmatch? What are the pros and cons?
Virtual crossmatch is a process assessing the result of solid phase and cell bases HLA antibody identification assays to predict, correlate to the result of physical crossmatch. Pros: (1) Increase the likelihood of crossmatch compatible donors to highly reactive patients.
(2) leads to successful transplantation to highly sensitized HD patients. Cons: (1) false negative allele specific antibodies/unique epitope not identified by single antigen beads [almost 20%].
(2) false positive with low levels of HLA antibodies, compromised donor cells and antibodies against denatured HLA antigens [5%].
References:
(1) UpToDate- evaluation of deceased organ donor.
(2) Morris AB, Sullivan HC, Krummey SM, Gebel HM, Bray RA. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era. HLA. 2019 Dec;94(6):471-481. doi: 10.1111/tan.13693. Epub 2019 Oct 17. PMID: 31515937; PMCID: PMC7341023.
(3) Peacock S, Briggs D, Barnardo M, Battle R, Brookes P, Callaghan C, Clark B, Collins C, Day S, Diaz Burlinson N, Dunn P, Fernando R, Fuggle S, Harmer A, Kallon D, Keegan D, Key T, Lawson E, Lloyd S, Martin J, McCaughan J, Middleton D, Partheniou F, Poles A, Rees T, Sage D, Santos-Nunez E, Shaw O, Willicombe M, Worthington J. BSHI/BTS guidance on crossmatching before deceased donor kidney transplantation. Int J Immunogenet. 2022 Feb;49(1):22-29. doi: 10.1111/iji.12558. Epub 2021 Sep 23. PMID: 34555264; PMCID: PMC9292213.
Thank you for your reply I agree with the virtual crossmatch, but what are the criteria required to perform a VXM in the index case? You have missed an important and essential requirement that is needed to perform a VXM.
What criteria are required to perform a VXM in the index case? Rapid crossmatching in sensitized recipients, from a cadaveric Donor, shown to improve outcomes in sensitized recipient. Identify best donor in short time.
What is “HLA null allele” meant and how would they affect the results of VXM? Null HLA alleles have identifiable DNA sequences with molecular typing, but do not express HLA products on the cell surface. Thus; the recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product, which may result in no no humeral rejection that is tolerable.
Information needed to support my decision
Donor and Recipient blood group should be known ,also cPRA and the sensitization of the patient like Blood transfusion ,vaccination history or history of transplantation should be known along with Viral serology of the donor and virtual cross match result. Cause of death in a road traffic accident-whether the patient was DCD OR DBD as it has impact on graft survival. Will you accept this offer and go ahead with the transplantation
Offer can be accepted but only after knowing the ABO compatibility and taking detailed history of the donor and ruling out infections in the donor and if no other option available. What is meant by virtual crossmatch? What are the pros and cons?
Virtual cross match is usually carried out for deceased donor transplants.In virtual cross match, anti-HLA antibodies detected by Luminex method are matched to HLA typing report of donor without doing the actual cross match. PROS:
It has resulted in improved organ allocation and
Less waiting times for transplantation.
HLA typing of donor is required just without the need of donor cells.
cold ischemia time is less and easily excludes unacceptable antigens. CONS:
False positive result may occur because of denatured HLA antigen on bead, low titer and/or non-complement binding antibodies.
SAB by luminex for recipient may need to be repeated every three months due to change in antibodies because of sensitization like pregnancy ,vaccination,infection, blood transfusion,and previous transplantation.
Lot of coordination between Immunology Lab personal and transplant team.
Cutoff values of MFI , thus, are different among laboratories not standardized. References: 1-Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017; 7(6): 339-348
2- Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188
-What information do you need to know to support your decision?
Blood grouping
CMV D/R status
Virtual cross-match
The cause of CKD5D if possible in the recipient
History of sensitization
-Will you accept this offer and go ahead with the transplantation?
Yes, depending on the cross-match which may be negative due to the excellent HLA match, and absence of DSA
Induction by basilliximab and maintenance on CNIs + MPA derivatives + prednisone
-What is meant by virtual cross-match? What are the pros and cons?
Virtual cross-match;
Solid phase antibody screening
Recipient serum is mixed with recombinant HLA antigens on beads; if the recipient has antibody specific to HLA antigen, this antigen is term unacceptable antigen
Pros:
permits transplant physicians to consider donor organs that would have not otherwise be available by the means of prospective cross-match strategy
Highly accurate
Improve organ allocations
Reduce cost
Reduce cold ischemia time
Facilitate KPD
Cons:
Use of antibody specificities from historical serum may not predict a cross-match results with certainty
Antibody specificities can be affected by pregnancies, blood transfusion, and transplant
False positive; low titre and or non-complement binding Ab, the may cause unnecessary exclusion of the donor
False negative; some antigens may not be represented on the beads
Source;
HLA typing & crossmatch; A comprehensive review by Ahmed Halwa et.al
Hand book of kidney transplantation 6 edition by Gabriel Danovitch
What information do you need to know to support your decision?
Sensitization history
Virology of donor and recipient
ABO typing
High resolution DNA-based HLA typing and the solid-phase assays
CPRA
Will you accept this offer and go ahead with the transplantation?
Yes, after risk stratification at the recipient center for kidney transplantation.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing. The American Society for Histocompatibility and Immunogenetics defines VXM test as an assessment of immunologic compatibility based on patient’s alloantibody profile compared with donor’s histocompatibility antigens. (1)
In contrast Physical crossmatch (PXM) tests, such as complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FCXM), require mixing of patient serum and donor cells, are labor intensive, and are logistically challenging
The goal of VXM is pretransplant risk stratification the output of VXM could be reported as a dichotomous positive or negative or as a probability value and has not been standardized.
Advantages
Increased sensitivity
May be performed with stored sera therefore shortening cold ischaemia time
Improves transplantation access for highly sensitized patients
Improves risk assessment for rejection Disadvantages
1- Denatured human leucocyte antigens on single antigen beads may lead to a false positive result
2- Requires more coordination between immunology lab personnel and transplant team A false negative virtual crossmatch can arise for a number of reasons.
– Incomplete typing of the donor,
– As well as donor specifc antibodies in the recipient serum against a unique HLA epitope which is not available on the SAB panel (2) False positives may also occur as a result of
– Antibodies directed at HLA epitopes that come about secondary to denatured HLA antigens on the SAB (3)
– Due to presence of null alleles, which are not expressed as antigens on the cell surface in vivo (4) Conclusion Implementation of VXM-based approach has resulted in statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes. Though there are considerable challenges, VXM is expected to be used more often in the future, depending on the transplant center’s tolerance of immunologic risk.
Ref
1- Bray R.A. The acceptability and application of virtual crossmatching in lieu of serologic crossmatching for transplantation. Virtual Crossmatch Work Group Report. Centers for Disease Control and Prevention.
2- Amico P, Honger G, Steiger J, Schaub S (2009) Utility of the virtual crossmatch in solid organ transplantation. Curr Opin Organ Transplant 14: 656–661.
3- El-Awar NR, Terasaki PI, Hajeer A et al (2010) A novel HLA class I single antigen bead preparation eliminates false positive reactions attributed to natural antibodies in the sera of normal males and pre-transplant patients. Hum Immunol 71(Suppl 1): S26
4- Tinckam KJ (2012) Basic methods. In: Chandraker A, Sayegh MH, Singh AK, eds. Core Concepts in Renal Transplantation. Springer, New York: 21–42
What information do you need to know to support your decision?
ABO status of both donor and recipient
If the patient has a living compatible donor since living donor kidney is associated with better outcome when compared to deceased donor kidney transplantation (1)
Virtual cross match (will be negative in this case)
history of sensitizing events before, cPRA of the recipient, to determine if the patient is sensitized or not which is important factor in deciding whether wet cross match is required or we can rely only on virtual cross match, this is especially in this female with possible history of pregnancy and blood transfusion
The type of the deceased donor DBD or DCD : DBD has the advantage over DCD as the circulation is maintained to the organs all the time, so it is associated with lower incidence of DGF but the overall graft survival is the same in both types of donors (2). A single center study reported 1 and 5 years graft survival of 87% and 82% for recipients of DCD, 91% and 86% for recipients < 60 years of DBD donors and of 80 % and 73% for recipients > 60 years of DBD donors (3)
CMV and EBV status of the donor and recipient and virology status of the donor
The cause of recipient renal failure and if there is a recipient contraindication for transplantation
Will you accept this offer and go ahead with the transplantation?
If there is no available compatible living donor, ABO status of the deceased donor is compatible with the recipient and virology (HCV, HBV, and HIV) is negative, recipient general condition permits transplantation I will go ahead with this transplantation.
What is meant by virtual crossmatch? What are the pros and cons?
Used for deceased donor recipients
By comparing anti HLA antibodies of recipient detected by luminex SAB to HLA profile of the donor. So it is a paper work
It is correlated well with FCM cross match and graft survival even in sensitized patients
Define unacceptable antigens so donors can be excluded, and allow identification of suitable donor
DSA may change over time due to sensitization from blood transfusion or pregnancy so luminex SAB should be repeated every 3 m
Wet cross match should be performed in only sensitized patients as there may be a new DSA that develop, this should be detected by wet cross match (positive FCXM, negative VXM), in non-sensitized recipient we can rely on VXM in proceeding in transplantation
A positive VXM with a negative FCXM can occur due to non-clinically significant low titer DSA that will not affect transplantation, so it is safe to proceed to transplantation
Advantages
It is correlated well with FCM cross match
Define unacceptable antigens so donors can be excluded
Correlated with good graft survival even in sensitized patient
Disadvantages
It may be affected by any cause of sensitization like pregnancy , blood transfusion, transplantation, Moreover antibodies may change over time so luminex SAB for recipient should be repeated every 3 m
References
1.2009 Annual Report of the U.S. Organ Procurement and Transplantation Network and the Scientific Registry of Transplant Recipients: Transplant Data 1999-2008. U.S. Department of Health and Human Services, Health Resources and Services Administration, Healthcare Systems Bureau, Division of Transplantation, Rockville, MD.
2.Beaupré RA, Morgan JA. Donation After Cardiac Death: A Necessary Expansion for Heart Transplantation. Semin Thorac Cardiovasc Surg 2019; 31:721.
3.Sánchez-Fructuoso AI, Marques M, Prats D, et al. Victims of cardiac arrest occurring outside the hospital: a source of transplantable kidneys. Ann Intern Med 2006; 145:157.
What information do you need to know to support your decision?
Sensitization history since the last screening is required (pregnancy, blood transfusion, abortion) of both the potential donor and recipient.
Vaccination schedules and recent infections must be considered.
When was the last screening of the potential donor?
Will you accept this offer and go ahead with the transplantation?
Yes, the absence of HLA and ABO mismatches added to the absence of antibodies against the donor makes the organ compatible and without the need for severe immunosuppression.
However, I would follow up more closely with DSA dosage by SAB after transplantation, as I do not have a recent crossmatch and DSA.
What is meant by virtual crossmatch? What are the pros and cons? Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests, patient anti-HLA antibody and donor HLA typing
A positive T cell CDCXM result is considered an absolute contraindication for transplantation because of its association with hyperacute/accelerated rejection. A positive B cell CDCXM result or a positive FCXM result increases the risk to an intermediate level and may need desensitization therapy prior to transplant but is not considered an absolute contraindication for transplantation, although regional differences in policies exist. It will reduce cold ischemia time
A high-percentage PRA implied a high probability of a positive crossmatch result. However, because CPRA is based on unacceptable antigens, kidneys with those antigens are not offered to a patient. Thus, an actual offer for a patient with high CPRA taking the unacceptable antigens into account implies a high probability of a negative crossmatch result. Importantly, although the broadness of HLA sensitization is determined by the CPRA and influences organ allocation, in terms of immunologic risk for the recipient, it is the donor specificity, not the broadness of sensitization, that is associated with allograft outcome.
What information do you need to know to support your decision?
Any history of recent sensitizing events? (blood transfusion, pregnancy or abortion).
Recent illness, infection, or vaccination.
What is the date of the latest blood sample from the potential recipient?
Will you accept this offer and go ahead with the transplantation?
Yes, provided that there is no new sensitizing event and the latest sample was within 3 months.
What is meant by virtual crossmatch? What are the pros and cons?
In virtual crossmatch (VXM), the immunologic compatibility between a patient and a donor is determined in silico (In a computerized model).
For nonsensitized patients who do not have circulating antibodies, physical crossmatch(PXM) results against any prospective donor can be assumed to be negative.
Many transplant centers have reported their successful results of proceeding to transplant based on VXM results without pretransplant PXM.
Waiting for PXM increases cold ischemia time which associated with delayed graft function, organ loss, and graft failure. However, depending on VXM may have its problems also, owing to limitations of the SAB assay—in defining the absence or presence of circulating antibodies against HLA.Examples are: 1-SAB assay may not contain beads for a particular specificity. 2- SAB manufacturing issues result in lot of variability 3- HLA structure present on the SAB assays differs between the 2 vendors that are currently available. 4-Shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen. 5-Inhibitory factors present in the patientserum—such as complement C1q—may interfere withantibody detection (prozone effect).
Currently, 18% of transplantations in USA is done depending on VXM. An analysis of US registry data identified 9632 kidney transplants between 2011 and 2018 using VXM and 71,839 using PXM.Cold ischemia time was significantly lower in the VXM group (mean 15.0 hours) compared with the PXM group (mean 16.5 hours). Importantly, mortality and death-censored allograft failure were similar.
References:
1-Principles of Virtual Crossmatch Testing for Kidney Transplantation Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani MuthukumarKidney Int Rep (2022) 7, 1179–1188;
2-Human leukocyte antigen typing and crossmatch: A comprehensive review Mohammed Mahdi Althaf, Mohsen El Kossi, Jon Kim Jin, Ajay Sharma, Ahmed Mostafa Halawa World J Transplant 2017 December 24; 7(6): 276-363
Both recipient and donor ABO blood group result will be needed
Both recipient and donor HLA pair matching result
The gender of the donor and if a female, the history of parity and blood transfusion
Virtual cross-match result since serum or lymphoid tissue are not available to do physical crossmatch like CDC of flow cytometry
Will you accept this offer and go on with the transplant?
YES, I will accept because
very good HLA matching
absence of DSA
What is virtual cross match
Virtual crossmatching is the method of detection of antibodies against the donor tissue by the comparison of the antiHLA antibodies of the recipient, as defined by Luminex, with the HLA of the donor. The presence of an antibodies will be reported as positive crossmatch
Pros of virtual crossmatch
it reduces the testing cost
it reduces the cold ischemic time
it has a high accuracy level
Cons of virtual crossmatch
the solid phase antigen bead (SAB) assay may not contain beads for a particular specificity.
SAB manufacturing issues result in so many variability
HLA structure present on the SAB assays differs between the two vendors that are currently producing it
shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen
The inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection and require pretreatment of the serum with heat, dithiothreitol, or ethylenediamine tetra-acetic acid, or dilution of the serum
References
William R Murrey, John Kanellis. Understanding crossmatch testing in organ transplantation: A case based guide for the general nephrologist.Nephrology. 2011;16:125-133
Gabriel M. Danovitch.Handbook of kidney transplantation. Sixth Edition.crossmatch testing for
Madhu C Mascharan, Sebastiaan, Thangamani Muthukumar. Principle of virtual crossmatch testing for kidney transplantation.Kidney International.2022; 7(6):1179-1188
What information do you need to know to support your decision?
Hematology. 1- Blood group and comprehensive metabolic profile including PT/APTT. 2- Extensive Viral serology 3- HLA of the Donor 4- cPRA of the recipient and history of Blood transfusion or transplantation 5- Depending on the above data, virtual crossmatch Kidney can be accepted in some circumstance after complete history and available laboratory result.
Virtual cross match. Crossmatch that involves a determination of the absence or presence of doner specific anti bodies in a patient by comparing the patients HLA antibody specificity profile to the HLA type of proposed donor without performing an actual crossmatch. It requires. 1. Complete tissue typing of donor and recipient. 2. Anti-HLA reports of recipient by solid phase assay method. Pros; Gaining acceptance for an alternative approach for crossmatch Does not require viable donor cell but totally relies on HLA typing of donor. Virtual crossmatch is a fast procedure and can save the time for transplantation. Reduce cold ischemia time. Accurate virtual crossmatch also important for donor Organ can be import Cones; False positive results of virtual crossmatch may arise where there are significantly low titer and/or non-complement binding antibodies. Different serum samples used for SAB versus crossmatch testing. An Antibody identifies that is specific to an allele that donor does not have.
Nephrology and Hypertension Board Review Phuong-Chi T. Pham, MD, FASN
What information do you need to know to support your decision?
1- Blood group to check the compatibility
2- blood culture and virology from the donor
3- HLA of the Donor
4- cPRA of the recipient and history of Blood transfusion or transplantation.
5- Depending on the above data, we can run the virtual crossmatch
Will you accept this offer and go ahead with the transplantation?
Yes, in certain circumstances, we can accept the virtual crossmatch.
What is meant by virtual crossmatch? What are the pros and cons?
The “virtual” crossmatch, which matches the patient’s antibody profile to the donor’s HLA type, has greatly decreased the requirement for a final “physical” crossmatch. It is used mainly in cadaveric kidney transplantation.
A computerized database predicts donors with a positive crossmatch based on a candidate’s inadmissible antigens. The computer does the cross-match, as UNOS does not give kidneys from donors with projected positive cross-matches.
Pros:
1-VXM reduces wait times and improves outcomes for sensitized transplant patients.
2-VXM enables transplant surgeons to examine donor organs that would not otherwise be accessible using a prospective crossmatch technique, making a possibly positive crossmatch a risk factor for donor selection.
3- Reduction of cold ischemic time
Cons:
1: Antibody specificity from serum samples older than six months cannot predict cross-matches.
2-Low titer and non-complement binding antibodies might cause false positive VXM findings, excluding prospective donors
3-The VXM may potentially yield erroneous negative findings since all prospective HLA donor antigens have been classified differently and cannot be appropriately represented.
4-VXM does not identify the HLA “Null” alleles.
1- Handbook of Kidney transplantation
2- Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017; 7(6): 339-348
Other informations needed
Blood grouping, virology screening ( HCV, HBV,EBV,CMV,HIV)
History of sensitization by Blood transfusion, pregnancy
HLA typing by luminex
Yes I will accept and proceed for transplantation
Virtual crossmatch is a technique to assess immunologic compatibility between recipient and potential donor by analyzing the results of their HLA typing and the recipient-owned anti-HLA antibody without using the donor lymphocytes
Pros
Virtual crossmatch shortens the cold ischaemia time and reduced delayed graft function, useful in cadaveric donors , shorten wait time and improve outcomes for sensitized patients.
Cons
Serum results must be within 3 to 6 months as antibodies vary with time
False positive results in presence of low title or non complement binding antibodies
False negative as it can’t detect null HLA alleles
1-
We have to if the recipient is sensitized
Previous blood transfusions, pregnancy, abortions, SOT…
2
DSA negative
Crossmach negative
==>
We can accept this donor and go forward transplantation
3-
The term “virtual” crossmatch refers to a process in which the clinician or laboratorian uses the results of two actual laboratory tests (the anti-HLA screening results and the HLA type of the donor) to deduce what the result of an actual crossmatch might be, should one be performed.
Strengths
○Fast test
○Important in case of sensitized patients
Weaknesses
●false-negative result if there are not enough antibodies binding to the RBCs to cause a reaction
●uncapable to identify null alleles
●may identify non-complement binding antibodies so this results of the increasing of excluded donors
What information do you need to know to support your decision?
Blood grouping of both donor and recipient,Infection screening including HIV,HBsAG,HCV ,any prior history of TB in donor,Detailed HLA typing of Both Donor and recipient,Luminex test of the recipient ,not later than 3 months reports should be available,H/0 sensitazation of recipient like blood transfusion,prior transplant,pregnancy H/o etc.
Will you accept this offer and go ahead with the transplantation?
yes donor should be accepted , No mismatch at HLA level and DSA negative .
What is meant by virtual crossmatch? What are the pros and cons?
Since the introduction of Luminex-SAB it is now possible to ‘virtually’ compare specifc anti-HLA antibodies in the recipient with the HLA profle of the donor. Tis is known as the virtual crossmatch. Te correlation of the virtual crossmatch with fow cytometry crossmatch is greater than 85%. It requires HLA typing of the donor and a recent anti-HLA profle of the potential recipient. To ensure a correct anti-HLA profle at the time of the transplant call, regular collection of sera every 3months is required for antibody screening via solid-phase assays, because antibody titres and specifcities can change over time.
A false negative virtual crossmatch can arise for a number of reasons. Incomplete typing of the donor, as well as donorspecifc antibodies in the recipient serum against a unique HLA epitope which is not available on the SAB panel, can give rise to a false negative result False positives may also occur, as mentioned previously, as a result of antibodies directed at HLA epitopes that come about secondary to denatured HLA antigens on the SAB . Yet another cause for a false positive virtual crossmatch is the presence of null alleles, which are not expressed as antigens on the cell surface in vivo .
One of the principal advantages of performing a virtual crossmatch is the detection of acceptable and unacceptable antigens . Tis avoids unnecessary shipping of organs resulting in less surgery delays, reduces cold ischaemia time, encourages cost savings and improved odds of transplanting highly sensitized patients.
This donor can be accepted being of young age, no significant medical history offered, absence of mismatch and DSA.
Information needed to be recognized is blood group, HLA typing , serology as HBV,HCV,HIV, CMV, EBV, and Toxoplasma , history of blood transfusion ,history of pregnancy and abortions, history of alcoholism.
Yes, I will accept this offer. Based on the mentioned information previously.
Virtual crossmatch is best explained by the prediction of presence of antibodies in the recipient serum to the proposed donor HLA thereby detecting the probability of rejection.
For more accurate results CDC and flow cytometry crossmatch by luminex can be performed. They provide better classification and determination of sensitization states of the recipient, consequently direct to the need for desensitization or not according to the MFI levels of donor specific antigens prior to transplantation process as well as the use of the suitable induction therapeutic agent.
The advantages are being cheap, fast, available, can be done even after donor’s death. While the drawback is mainly being less accurate so it is less reliable.
This donor can be accepted after doing virtual crossmatch using the data of HLA report.
History of blood transfusion and previous sensitization to the recipient is required beside full clinical history of the donor.
Virtual crossmatch is the process of assessing the result of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch.
thank you
41-year-old CKD 5 female
Received a deceased kidney offer
000 mismatch
No DSA.
The donor was 34-year-old, died in a road traffic accident. No past medical history with excellent kidney function.
There was no blood sample or lymphoid tissues available to run the crossmatch.
● What information do you need to know to support your decision?
Blood group
History of pregnancies and abortions
History of Blood transfusion or transplantation
Donor HLA typing
● Will you accept this offer and go ahead with the transplantation?
With negative cross match and DSA I will accept this donor
● What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests : patient anti-HLA antibody and donor HLA typing.
● Pros :
☆ It is useful in cadaveric transplantation work up.
☆ Shorter wait time
☆ Improved outcomes for sensitised transplant recipients.
☆ Permits transplant physicians to consider donor organs that would not otherwise be available by means of a prospective crossmatch strategy.
● Cons :
☆ A VXM does not identify ‘null alleles’
☆ False positive results of may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors
☆ It can give false negative results due to the fact that the list of all potential HLA donor antigens have been classed differently
What information do you need to know to support your decision?
ABO blood grouping, HLA typing, Latest Luminex test for DSA in donor blood best, Virology screen HBV, HCV, HIV, CMV, EPV, Detailed history of malignancy.
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept the offer and go ahead with the transplantation
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch is a risk assessment tool used to ascertain the presence of HLA antibodies in the recipient’s serum and to determine the potential crossmatch results with an available donor virtually. Recipient sensitization towards different HLA can be predicted before performing actual CDC and Flow cytometry crossmatch. For a virtual crossmatch, we first analyse and titrate the levels of anti-HLA antibody in the recipient’s serum by means of Luminex platform. The level of these antibody is measured in terms of Mean Fluorescence Intensity (MFI). MFI >1000-2000 is considered highly significant which has the potential to convert a CDC/ Flow cytometry crossmatch positive. These antibody levels are then directly corelated to donor’s HLA antigen profile and a virtual crossmatch is established.
Pros: 1. Used in case of both the sensitized and non-sensitized patients
2. Predicts actual flow cytometry cross match results, facilitating rapid allocation of organs in highly sensitized recipients.
3. Some studies have shown the statistically significant reduction in cold ischemia time with the use of virtual crossmatch.
4. Virtual cross match is possible both at the time of organ allocation and after organ allocation.
Cons:
Less reliable compared to another crossmatch testing available
Reference
1. Clifford Sullivan H, Krummey SM, Gebel HM, et al. Physical crossmatching vs virtual crossmatching: the end of an era? or why give up a good thing?. Hum Immunol. 2020;81:401-406.
2. Rao, Prakash; Deo, Dayanand; Marchioni, Misty; Harris, Patricia. 117.4: The virtual crossmatch: A useful tool to improve organ allocation. Transplantation 103(11S):pS12. 2019.
Q1: We need the BG of both the recipient and donor for ABO compatibility and their HLA typing. In addition, a recent Luminex test of the recipient and the history of sensitizing events like pregnancy or transfusion screening for viral infections and its history are necessary.
Q2: Yes, they are zero mismatches, no DSA and if the result
of VXM is negative and ABO compatible, they are a suitable donor.
Q3: virtual cross-match is not a physical cross match but
by using donor HLA and antibody screening of recipient by Luminex, one could
determine the result of cross-match. For virtual crossmatch at least one recent
result less than 3-6 months should be considered.
False positive: low-titer or non-complement binding
antibodies results in the wrong exclusion of potential donors.
False negative: due to misclassification of HLA Ags.
virtual crossmatch does not include null alleles of HLA. Null HLA alleles are
determined by molecular typing but do not express them on the cell surface.
When a null allele in the recipient is considered fully expressed, especially
in HSCT, there is the risk of developing DSA which can affect future
transplantation.
Advantages of VXM: shorter cold ischemic time in deceased
donors.
Disadvantages of VXM: false positive and false negative
results as mentioned earlier
1. Choose the correct answer regarding Null HLA alleles
A. It could be missed on VXM
B. It is unexpressed HLA but identified by molecular testing
C. More important in renal transplantation
D. DSA against unidentified null alleles can cause an immunological challenge
E. All the above
VXM can not identify null allel as expression of allel is not checked in VXM
A true
B is true as THIS STATEMENT is the definition of null allel
C need some explanation from proff
D why DSA will develop if null alllel is not expressed ?
• What information do you need to know to support your decision?
In Deceased donor transplantation
The following should be checked including
1. ABO blood grouping
2. HLA typing
3. DSA in donor blood best technique is by luminex recent one
4. Virology screen HBV, HCV, HIV, CMV, EPV
5. Proper history and history of cancers
6. History of active or old infections
• Will you accept this offer and go ahead with the transplantation?
First i need to check for ABO compatability
This Deceased donor is 000 mismatch with no DSA even in absent cross match
I shall accept this Transplant
What is meant by virtual crossmatch? What are the pros and cons?
It is a virtual or not physical cross HLA cross match between donor and recipients to detect possible antibodies in recipients blood
Regarding Pros : rapid test offer a good prediction of the prognosis of the tx even before true cross match
Shorten cold ischemia time
Regarding Cons
1. Not a quite reliable test especially if done more than e months
2. False positive in case of non complement binding antibodies or low titres of Anti HLA antibodies
3. False negative especially in null alleles where there is no expression of HLA on cell surface
Q1- What information do you need to know to support your decision?
I need to know
A- Blood group compatibility.
B- Sensitization state ( PRA% , HLA typing , any previous crossmatch, history of previous transplantation, blood transfusion, revious pregnancy)
C- Underlying cause of renal failure .
D- Renal biopsy if present .
E- Virology screen hepatitis B,C. HIV, CMV , EBV, herpes SIMPLEX .
F- Malignancy history .
G- We can do virtuall crossmatch if blood sample is not available .
Q2- Will you accept this offer and go ahead with the transplantation?
Yes, I do accept this offer as the as there is 000 missmatch, no DSA , and young age donor And no obvious contra indication .
Q3- What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatching
In virtual crossmatch (VXM), both donor HLA typing and solid phase antibody screening are utilised together. It is not real a crossmatch of mixing serum and lymphocytes. The data is used to forecast the actual in vitro crossmatch results by “mixing” identified antibody specificities of recipient serum with donor HLA antigens .
1- The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
2- VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a prospective crossmatch strategy, and thereby, allows to consider a potentially positive crossmatch a risk factor for donor selection .
3- Titres, specificities, and presence or absence of antibodies could significantly vary over time. Thus, the use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty. The VXM should, therefore, be done considering all available serum results including at least one recent within less than 3-6 mo for a given patient.
4- False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors .
5- The VXM can also give false negative results due to the fact that the list of all potential HLA donor antigens have been classed differently and, therefore, can not be correctly represented .
6- The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
7- VX-M does not identify the HLA “Null” alleles.
Reference:
Aslam S., Buggs J., Wyatt K., et al. The impact of virtual crossmatch on cold ischemic times and outcomes following kidney transplantation. Ann M Surg. 2021;87:109–113. doi: 10.1177/0003134820942180. [PubMed] [CrossRef] [Google Scholar]
⭐ ⭐ in the present scenario, no blood sample to perform wet cross match…so we can depend on Virtual cross match or not ….it depends on:
_History of recent sensitization as blood transfusion , infection or even vaccination that can produce newly formed DSA which necessitates wet cross match to confirm that we can proceed to transplantation.
_ Also , we need to know the blood groups of both the donor and recipient.
⭐ ⭐ based on that 000 mismatch and negative DSA, that means that negative VXM (depending on HLA typing of the donor and DSA detection in the recipient by luminex single antigen bead).
We can proceed to transplantation if no recent hx of sensitizing event..
_If postive hx …that means false negative VXM and postive DSA (which will have postive FCXM).
_Null HLA antigens are HLA molecules, not expressed on cell surface and detected only by microscopic or high molecular diagnosis.
_It can induce DSA, and have immunological consequences especially in HSCT more than SOT.
⭐⭐pros:
_virtual cross match is rapid, decrease cold ischemia time in deceased donor and nor require essential transfer of samples across long distance.
⭐ Cons:
_give false negative results is recent sensitizing event, do DSA should be repeated every 3 months while on the waiting list or essentially requiring wet cross match.
The important information required is:
Blood group of donor
Any co-morbidity such as diabetes, hypertension, CVD
Viral profile such as Hepatitis B, C, HIV, CMV
Past history of malignancy
Would you accept this offer?
Yes
Virtual cross match
Virtual Crossmatch is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch.
Pros: Shorter time to transplantation
Cons: Less reliable compared to other crossmatch testing available
1- We need to know the Blood group to check ABO compatibility, as well as tissue typing and viral serology.
2- since this is a deceased donor offered, probably ABO compatible (directly transplantable ?)
3- As the name explains, it is not a physical crossmatch. Rather, it compares the antibodies present in the recipient against the HLA of the potential donor.
VXM is easy and quick but may not correlate with the last condition, sensitization may alter results. In physical CMX the actual state is reflected.
——
https://www.kireports.org/action/showPdf?pii=S2468-0249%2822%2901213-X
What information do you need to know to support your diagnosis:
We need information about,
1. HLA typing,
2. Blood grouping,
3. Virtual cross match report,
4. Viral serology report,
5. The cause of renal failure in recipient,
6. Previous transplantation,
7. DSA level.
Will you accept this offer and go ahead with the renal transplantation:
I will accept this donation as there is no such high risk and contraindication.
What is meant by virtual cross-match and what are pros and cons:
The virtual cross-match is the process of assessing the result of solid phase and cell based HLA antibody identification assays to predict the result of physical cross-match.
In contrast to physical cross-match, the virtual cross-match does not need viable donor cells but relies on complete HLA typing of the donor and current antibody assessment of the recipient.
Reference:
1. Roberta Callus, Jesmar Buttigieg, Andrei Agius Anastasi, Ahmed Halawa. Basic concepts in kidney transplant immunology British Journal of Hospital Medicine, January 2017, Vol 78, No 1.
2. Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339.
What information do you need to know to support your decision?
The current status of the donor needs to be known … the hemodynamic condition, amount of blood loss from the accident (if any), biochemical parameters and urine output (within the ICU). In addition, we need to know the blood group of both the donor and the recipient as well as the presence of any active infections.
Will you accept this offer and go ahead with the transplantation?
Yes, we may proceed with the transplantation if there are no absolute contraindications. There is 000 mismatch and there is no DSA – the chance of rejection is low. We also need to ensure that the primary disease of the recipient is controlled – so that the graft does not fall victim to the systemic insults that has been damaging the native kidneys of the patient.
What is meant by virtual crossmatch? What are the pros and cons?
Unlike a physical crossmatch or PXM, a virtual crossmatch or VXM involves comparing and matching (on pen and paper or computer software) between the HLA Antigens of the donor and the HLA Antibodies of the recipient to analyse whether they may cross-react if this donor kidney is transplanted to this recipient.
PROs
CONs
Reference:
Jaramillo, Andrés PhD1; Reddy, K. Sudhakar MBBS2; Heilman, Raymond L. MD3. Using the Virtual Crossmatch to Allow for Safer and More Efficient Kidney Transplantation of Highly Sensitized Patients. Transplantation 104(6):p 1121-1122, June 2020. | DOI: 10.1097/TP.0000000000002925
What information do you need to know to support your decision?
– ABO compatibility.
– HLA compatibility
– Any History of sensitizing events for both donor and recipient.
– Recent anti-HLA antibodies profile for the recipient.
– Virtual cross matching.
– Virology screening CMV, EBV, HIV.
Will you accept this offer and go ahead with the transplantation?
Yes, this donor can be accepted as is a good match and no DSA.
What is meant by virtual crossmatch? What are the pros and cons?
– VXM is a risk assessment tool, determine the immunologic compatibility between a recipient and a donor by analyzing and comparing the results of 2 independently done laboratory tests—patient anti-HLA antibody and donor HLA typing.
-can predict actual crossmatch results based on antibody specificity and strength detected by solid-phase assays.
-need an up-to-date HLA antibody testing of recipients and complete HLA typing of donors for accurate predictive results.
Pros:
– It improved organ allocation efficiency.
– Define unacceptable antigens
– Reduced testing costs.
– Shorter wait times and cold ischemia time
– more sensitive than PXM to detect the presence of DSA.
– Does not require a viable cell.
– a possible positive crossmatch is a risk factor for donor selection.
Cons:
– The use of antibody specificity from historical sample (earlier than 6 months) could not predict a crossmatch with certainty.
– False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies or denatured human leukocyte antigen on SAB.
– The result varies according to the laboratory’s MFI cutoff values
– False negative results due to:
– the list of all potential HLA donor antigen, cannot be correctly represented.
– HLA structure present on the SAB assays differs between the 2 vendors that are currently available
– Shared epitopes.
– Inhibitory factors present in the patient serum may interfere with antibody detection (prozone effect).
– VXM does not identify the HLA “Null” alleles.
Reference:
Human leukocyte antigen typing and crossmatch: A comprehensive review Mohammed Mahdi Althaf, Mohsen El Kossi, Jon Kim Jin, Ajay Sharma, Ahmed Mostafa Halawa World J Transplant 2017 December 24; 7(6): 276-363
– ABO compatibility
– Present DSA
– History of presensitization (pregnancy, blood transfusion)
– History of donor i.e- H/O malignancy, DCD or DBD
If there is ABO compatibility i will accep this donor as there is 000 mismatch, no DSA and negative VXM.
– VXM is a risk assessment tool, determine the immunologic compatibility between a recipient and a donor by analyzing and comparing the results of 2 independently done laboratory tests patient anti-HLA antibody and donor HLA typing.
-A virtual crossmatch can predict actual crossmatch results based on antibody specificity and strength detected by solid-phase assays.
PROS
– Quick (shorter wait times)
– Tests against a large number of fixed and consistent HLA antigens
– Can be performed at the time of donor identification
– Consider a potentially positive crossmatch depending on a risk factor for donor selection
CONS
– Does not identify the HLA “Null” alleles (are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface).
– The use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty
– False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies
– False negative results due to the fact that the list of all potential HLA donor antigens have been classed differently
-The results from are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well
1- Blood group for both donor and recipient .
2- viral status for both the donor and recipient
3- History of sensitization ( blood transfusion , pregnancy .. etc )
4- We have to do vXM
5- History of previews infection or malignancy .
Yes I will accept this donor , 0 0 0 MM with No DSA
Virtual crossmatch involves comparison of recipient’s anti-HLA antibody profile with the HLA antigens of the prospective donor.
If the recipient is not sensitized against the donor, transplantation can be done without a final FCXM.
Pros:
1- quickens the transplantation process and reduces costs.
2- acceptable recipients are quickly identified,
3- cold ischemia time is reduced,
4- unnecessary graft shipments are avoided
5- the chance that a recipient with high sensitization gets transplanted is increased
cons :
1- false negative result if DSA against a rare allele is present
2- Given its high sensitivity, L-SAB can also detect clinically unimportant DSA, leading to some recipients missing the chance to be transplanted.
3- the prediction of a positive FCXM by vXM is affected by the MFI value used and the DSA type
References
1) Crossmatching in Renal Transplantation by Non-Immunologists for Non-ImmunologistsMartin Chari,1,2 Mohsen El Kosi,2,3 Jon Kim Jim,2,4 Ajay Sharma,2,5 Ahmed Halawa2,62) Hand book of kidney transplantation 6th edition
· ABO group of donor and recipient
· cadaver donor type – DBD/DCD; vitals and last ser creatinine before retrieval; cold ischemia time since retrieval
· viral serology of donor & recipient (HIV, Hepatitis B&C, CMV, EBV)
· Recipient’s clinical details:
o cause of CKD; infections and malignancies
o h/o sensitization (blood transfusion, pregnancy, previous transplant)–
· HLA typing of donor and recipient;
· Complete antibody – SAB assay (by Luminex-NGS) report of recipient, preferably with in last 3 months.
· C-PRA % of the recipient
· Virtual crossmatching – as blood / tissue of donor not available
34Years young donor, no significant past medical history, excellent kidney function, 000 mismatch, no DSA – the offer is well acceptable for this recipient. We should go ahead with the transplant, provided the organ is well preserved and within the allowable cold ischemia time.
VIRTUAL CROSSMATCHING:
· The VXM is defined as “An assessment of immunologic compatibility based on the patient’s alloantibody profile compared to the donor’s histocompatibility antigens”.
· It is a very specific assessment for donor-specific anti-HLA antibody sensitization by combining the HLA typing of the donor with the detailed antibody profile (solid phase assy, preferably Single Antigen Beads analysis) of the recipient to determine HLA compatibility.
· In contrast to a physical crossmatch (donor cell-based CDC / Flowcytometry) methods, the VXM does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment (SAB assay) of the recipient, may be done in 2 different labs in different time.
· Thus, the VXM can be performed in minutes which allows for faster transplant decisions thereby increasing the likelihood that organs can be shipped across significant distances yet safely transplanted.
Pros (Advantage): VXM has a significant advantage over physical crossmatching
· It has been acceptable as the only pretransplant “crossmatch” necessary in many studies
· Avoid unnecessary delay in physical crossmatching (cumbersome and time taking in transporting donor sample to the recipient’s centres for testing), hence shortens the cold ischemia time – avoid wastage of organs, improve clinical outcome in recipients. Sometimes adequate donor samples may not be available for test in subsequent labs, if the first recipient does not match with.
· Increased sensitivity/ ability to detect donor-specific HLA antibodies
increase donor pool and more likelihood of finding compatible donors for highly reactive patients
· Allow successful transplantation of more dialysis patients who are highly sensitized to HLA allo-antigens – increase transplant accessibility and reduce time on waiting list
· Improves risk assessment for transplant rejection, thus can plan suitable induction and immunosuppression protocol
Cons (disadvantages) of VXM)
· Requires coordination between the immunology lab and the transplant team
· denatured antigens, nonexposed epitopes, or bead abnormalities not excluded, can lead to false positive VXM
· MFI cut-off for positivity is not consistent in different lab / methods
· The antibody profile can change with time, so wait-listed patients need to have repeat SAB /DSA profile done every 3months
· More costly
References:
1. Morris AB, Sullivan HC, Krummey SM, et al. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era. HLA 2019 Dec; 94(6): 471-481.
2. Bhaskaran MC, Heidt S, Muthukumar T, et al. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney International Reports 2022 Jun; 7(6): 1179-1188.
What information do you need to know to support your decision?
I would information regarding
Will you accept this offer and go ahead with the transplantation?
Yes, I would go ahead with this transplant, provided the virtual cross match is negative.
If this recipient has not sensitization history and if cPRA is low, then the transplant can proceed provided the virtual crossmatch is negative.
What is meant by virtual crossmatch(VXM)? What are the pros and cons?
The American Society for Histocompatibility and Immunogenetics defines VXM test as an assessment of immunologic compatibility based on patient’s alloantibody profile compared with donor’s histocompatibility antigens.
pros:
cons:
The test may not be correct in two circumstances
other con would cost and practicality of performing the recipient antibodies every three months.
Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
Blood group
virology screen
virtual cross match
HLA typing
flow cytometry B and T lymphocytes
Yes, because excellent renal function no DSA , no contraindcation
.
is the process comparing the recipient antibody to the donor HLD typing as predication of the actual crossmatch.
Q 1.What information do you need to know to support your diagnosis?
I will be needing information about,
1. HLA typing,
2. Blood grouping,
3. Virtual cross match report,
4. Viral serology report,
5. The cause of renal failure in recipient,
6. Previous transplantation,
7. DSA level.
Q 2. Will you accept this offer and go ahead with the renal transplantation?
I will accept this donation as there is no such high risk and contraindication.
Q 3. What is meant by virtual cross-match and what are pros and cons?
The virtual cross-match is the process of assessing the result of solid phase and cell based HLA antibody identification assays to predict the result of physical cross-match.
In contrast to physical cross-match, the virtual cross-match does not need viable donor cells but relies on complete HLA typing of the donor and current antibody assessment of the recipient.
The correct answers are,
A. true
B. true
C. false
D. true
E. false
Chose the correct answer regarding VXM
Chose the correct answer regarding virtual crossmatch.
Ans; A.B, and D.
What information do you need to know to support your decision?
(i) ABO blood group of pair
(ii) Virtual cross match should be done
(iii) History of any chronic illnesses, malignancies
(iv) HLA typing of recipient and anti HLA Ab testing
(v) Flow cytometry of B and T lymphocytes
(vi) Any risk of sensitization eg. blood transfusion, pregnancies
(vii) Viral screening: HIV,CMV,EBV
Will you accept this offer and go ahead with the transplantation?
I shall accept this donor as 000 HLA miss match, excellent kidney function , and absence of DSA, I shall go for ABO compatibility and virtual cross match before transplant.
What is meant by virtual crossmatch? What are the pros and cons?
In this process comparing the recipient antibody from solid phase testing to the donor HLA typing as a prediction of the actual crossmatch.
Predicts presence of donor specific antibodies using solid phase without an actual crossmatch, three monthly collection of sera is done for antibody screening via solid phase assay to ensure the right anti HLA profile at the time of transplantation. Compares recipients’ HLA ab to donor HLA type to predict cross match result.
What are the pros of virtual crossmatch:
(i) Decreased investigation cost
(ii) Shortening of cold ischemic time
(iii) Facilitates kidney paired donation
(iv) The virtual crossmatch ensures timely allocation of organs
What are the cons of virtual crossmatch:
(i) Denatured HLA on single antigen beads is done and which may lead to a false positive result
(ii) Requires more coordination between immunologist and transplant team.
(iii)Is not a cent percent accurate and an actual crossmatch be performed as well.
Reference:
1. Roberta Callus, Jesmar Buttigieg, Andrei Agius Anastasi, Ahmed Halawa. Basic concepts in kidney transplant immunology British Journal of Hospital Medicine, January 2017, Vol 78, No 1.
2. Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339.
What information do you need to know to support your decision
Deceased kidney donor
We must to know if it is DBD / DCD
Time of ischemia
Blood group cross match cPRA and HLA Typing
infections Hepatitis CMV,EBV ….
Full assessment of the Recipient including cardiac assessment,chronic infection including hepatitis,TB,EBV CMV
Repeating Blood group cross match cPRA HLA typing DSA
Will you accept this offer and go ahead with the transplantation?
Yes , I will accept such young deceased donor with 000 mismatching and excellent kidney function
What is meant by virtual crossmatch? What are the pros and cons?
Virtual Crossmatch is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch.
The virtual crossmatch does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient. Thus, the VXM can be performed in minutes which allows for faster transplant decisions thereby increasing the likelihood that organs can be shipped across significant distances yet safely transplanted.
Virtual crossmatch (VXM) analysis included serological and epitope identification. The serological analysis compared the serological HLA typing and antibody detection to identify the serological donor-specific antibody (sDSA).
I would like to know Blood group of donor and recipient
Any recent sensitization event for recipient.
I will accept this offer as 000 mismatch , No DSA
The term “virtual” crossmatch refers to a process in which the clinician or laboratorian uses the results of two actual laboratory tests (the anti-HLA screening results and the HLA type of the donor) to deduce what the result of an actual crossmatch might be, should one be performed. If a candidate is found to have antibody against an HLA antigen for which the donor is mismatched with the candidate (DSA), and if the “strength” of the antibody is thought to be sufficient, there is some predictive value with a positive or negative actual crossmatch. The correlation of this DSA or “virtual crossmatch” naturally depends upon what kind of crossmatch is anticipated.(up to date)
What information do you need to know to support your decision?
Blood group and ABO compatibilitycrossmatch for the recipient – CDC and Flow XMLuminex- SAB for Anti-HLA Ab.Virological screening : HIV, Hepatitis , Syphilis ,CMV, EBV, VZVscreening for current active infectionsStructural assessment such as ultrasonography of kidneys and CTA 6 for donor,Will you accept this offer and go ahead with the transplantation?
Young Donor and no mismatches 000 HLA, good kidney function and absence of DSA. I will accept this donor.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch can now predict actual crossmatch results based on antibody specificity and strength detected by solid phase assays.
Pros
significantly improved organ allocation efficiencyreduced testing costsreduced cold ischemia timereduced time needed for testing after the organ arrives at the transplant centerfacilitated kidney paired donation (KPD) programsCons
Can give a false positive or negative result.Does not identify an HLA (Null) alleleAccurate prediction relies heavily on up-to-date HLA antibody testing of recipients and complete HLA typing of donors including HLA-A, B, C, DRB1, DRB3/4/5, DQA1, DQB1, DPA1, and DPB1.
What information do you need to know to support your decision?
· Blood grouping
· CDC Cross match
· Flow cytometry cross match
· History of sensitization
· Viral screen including Hep B& C , HIV, CMV, Herpes Simplex
Will you accept this offer and go ahead with the transplantation?
Yes , I will accept this offer subject to DSA levels.
What is meant by virtual crossmatch? What are the pros and cons?
Physical crossmatch tests, such as complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FCXM), require mixing of patient serum and donor cells, are labor intensive, and are logistically challenging.
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing. The goal of VXM is pretransplant risk stratification.
The Pros
Sensitivity similar to FXCM
Less ischemia time
Less risk of hyperacute rejection and early ABMR
Detection of acceptable and unacceptable antigens
The Cons
False positive results can happen
False negative due to incomplete HLA typing of donor and DSA in recipient against Epitope not available on SAB
Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348
What information do you need to know to support your decision?
ABO compatibility between donor and recipient.
Prior sensitisation episodes in the recipients.
Cause of the CKD.
Virology status-HepB, HepC, HIV, CMV
HLA typing
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept young donor no cross match and no DSA. Proceed with virtual cross match.
What is meant by virtual crossmatch? What are the pros and cons?
VXM applies the assessment of immunological compatibility between donor and recipient by use of 2 independently physically done patient anti-HLA antibody and donor HLA typing.
Pros: Shorter waiting time and improved outcomes for sensitised patients.
Cons: False positive results can occur when there are low titers or non-complement binding antibodies. False negative can occur when the list of all potential donor HLA antigens are classified differently thus incorrectly represented. VXM are not 100% accurate and should thus be followed by actual crossmatch. VXM does not identify null HLA alleles.
References
Human leukocyte antigen typing and crossmatch: A comprehensive reviewMohammed Mahdi Althaf, Mohsen El Kossi, […], and Ahmed Mostafa Halawa
Principles of Virtual Crossmatch Testing for Kidney Transplantation
Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani Muthukumar4,5
Information needed to support the decision:
Accept the donor or not:
Virtual cross-match:
References:
blood grouping and virtual cross match and CDC.
sensitization event in the recipient sus as blood transfusion and previous transplant.
virology screening such as hepatitis B.C.HIV.EBV and CMV.
any previous PRA%.
any previous crossmatching.
any history of malignancy.
41. Aslam S., Buggs J., Wyatt K., et al. The impact of virtual crossmatch on cold ischemic times and outcomes following kidney transplantation. Ann M Surg. 2021;87:109–113. doi: 10.1177/0003134820942180. [PubMed] [CrossRef] [Google Scholar]
Null allels : some allels with gene mutation contain sequence defects preventing normal antigen expression on cell surface. They are non immunogenic and of less significance in solid organ transplantation.
In case of deceased donor transplantation, we perform VXM. Donor HLA typing is required and recipient solid phase assays as well.
-DSA may change due to sensitization so Luminex SAB should be repeated / 3 months..
-Wet CM should be performed in sensitized patients considering possibility of new DSA, (positive FCXM, negative VXM).VXM could be enough in non-sensitized recipients.
There are many spelling errors making it difficult to read
1. What information do you need to know to support your decision?
-Blood group.
-Recipient HLA-Abs by SAB techinque
-Donor HLA-Ags
Will you accept this offer and go ahead with the transplantation?
Yes,because 000 mismatches , no DSA and donor age is suitable for recipient
What is meant by virtual crossmatch?
A test to determine the immunologic risk of a recipient with a potential donor by ensuring that there are no transplant-relevant circulating antibodies in the recipient directed against donor antigens.
What are the pros and cons?
Pros:
-It provides a quick assay for high-resolution HLA typing that is available for deceased donors.
Cons:
– limitations of the SAB assay—in defining the absence or presence of circulating antibodies against HLA:
1.the SAB assay may not contain beads for a particular specificity .
2.SAB manufacturing issues result in lot-to-lot variability.
3.HLA structure present on the SAB assays differs between the 2 vendors that are currently available,
4. shared epitopes—antibody targets .
5. inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect) and require pretreatment of serum .
Thus, the failure to detect an antibody on a SAB assay is not a proof of absence of that antibody in circulation.
Reference:
-Madhu C et al .Principles of Virtual Crossmatch Testing for Kidney Transplantation. NIH.2022 Mar 15. doi: 10.1016/j.ekir.2022.03.006
I like your statement that ‘the failure to detect an antibody on a SAB assay is not a proof of absence’
1-What information do you need to know to support your decision?
the basic information after referral to organ procurement organization opo
Patient’s name, age, date of birth, sex, race, and medical record number
Patient’s admitting diagnosis
Ventilator status of the patient
Neurologic status of the patient
Plan for brain death testing
Patient’s current vital signs, labs, and medications
Patient’s past medical history
Family’s understanding of the patient’s event/status
Initial donor screening — The organ donor referral from a hospital will be initially screened to exclude obvious patients who cannot be donors.
Common screening questions include:
What is the age of the patient?
Is the patient currently on a ventilator?
Does the patient have an active malignancy or a history of malignancy?
Are brain death examinations planned?
Is the family ready to withdraw support?
Immediate contraindications to donation — The following patient characteristics are generally considered to be absolute contraindications to deceased organ donation:
Age >80 years
Not on a ventilator
History of active metastatic cancer
History of active hematologic malignancy
History of active melanoma
History of Creutzfeldt-Jakob disease
Routine blood and urine tests — The following laboratory tests are performed on all deceased donors:
Complete blood count
Serum electrolytes, blood urea nitrogen (BUN), and creatinine
Liver function tests
Urinalysis
Arterial blood gas (ABG)
Prothrombin time (PT)/international normalized ratio (INR) and activated partial thromboplastin time (aPTT)
Blood, sputum, and urine cultures
ABO blood typing ABO blood typing must be performed on two different blood samples, drawn at separate times, with congruent results. ABO subtyping must be performed on all donors with blood type A to determine if the blood type is non-A1, since blood type A, non-A1 donors (eg, blood type A2) can be used for low titer blood type B recipients. ABO subtyping can only be reported if there is congruence between the two samples. The blood type must be verified by two qualified health care professionals, with source documentation, and reported to UNOS prior to the match run.
Histocompatibility testing — All deceased donors must have human leukocyte antigen (HLA) typing of antigens A, B, Bw4, Bw6, C, DR, DR51/52/53, DQA1, DQB1, and DPB1. Many OPOs send the donor’s blood samples to a reference lab for HLA typing. However, if the donor is at an academic hospital or transplant center, HLA testing is typically performed at the institution’s tissue typing laboratory. The results must be available before any kidney or pancreas is offered to the transplant centers on the match run. The HLA results must be available before final acceptance of an offer for heart or lung donors, if required by the transplant program. The OPO provides donor blood or lymph nodes to the transplant centers for direct crossmatching for kidney donation
Infectious disease testing — All organ donors are tested for various infectious diseases that can be transmitted to a recipient. Infectious disease testing requirements include the following:
HIV antibody (anti-HIV) donor screening test or HIV antigen/antibody (Ag/Ab) combination test
HIV RNA nucleic acid amplification test (NAT)
Hepatitis B surface antigen (HBsAg) donor screening test
Hepatitis B core antibody (anti-HBc) donor screening test
Hepatitis B DNA NAT
Hepatitis C virus antibody (anti-HCV) donor screening test
Hepatitis C RNA NAT
Cytomegalovirus antibody (anti-CMV) donor screening or diagnostic test
Epstein-Barr virus antibody (anti-EBV) donor screening or diagnostic test
Syphilis donor screening or diagnostic test
Toxoplasma immunoglobulin G (IgG) antibody test
2-Will you accept this offer and go ahead with the transplantation?
NO
There was no blood sample or lymphoid tissues available to run the crossmatch.
Histocompatibility testing — All deceased donors must have human leukocyte antigen (HLA) typing of antigens A, B, Bw4, Bw6, C, DR, DR51/52/53, DQA1, DQB1, and DPB1. Many OPOs send the donor’s blood samples to a reference lab for HLA typing. However, if the donor is at an academic hospital or transplant center, HLA testing is typically performed at the institution’s tissue typing laboratory. The results must be available before any kidney or pancreas is offered to the transplant centers on the match run. The HLA results must be available before final acceptance of an offer for heart or lung donors, if required by the transplant program. The OPO provides donor blood or lymph nodes to the transplant centers for direct crossmatching for kidney donation
3-What is meant by virtual crossmatch? What are the pros and cons?
is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of aphysical crossmatch. Based on this data review, donor organ offers can be accepted or declined based on the predicted risk of transplan
Virtual Crossmatching in Kidney Transplantation, Shiraz Experience in Development of a Web-Based Program2021Results: The average time for a manual VXM was 30 minutes per patient, while the virtual cross web-based program took 5 minutes per patient. In 12% of the manual VXM cases, a secondary review of data improved final results. In two manual virtual crossmatches, the VXM results had errors in matching recipient antibodies with the donor HLA typing that could affect the final decision for transplantation.
Conclusion: In conclusion, a web-based VXM program that assesses HLA data can accurately perform a VXM with fewer human errors. It is especially true for highly sensitized candidates.
I do not agree that you will not accept this kidney. This is a real-life situation.
What information do you need to know to support your decision?
· Blood grouping and crossmatch(CDC &FCXM) are needed.
· History of blood transfusion and sensitization in regard to potential recipient.
· Virology screening, including CMV, EBV, HIV, HSV, hepatitis B&C.
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept this offer provided no DSA and 000 mismatch.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatching refers to the comparison of the anti-HLA antibodies of the recipient, as defined by Luminex, with the HLA of the donor. Antibodies are defined against HLA class I and II antigens(1).
Virtual crossmatching ;the pros and cons(2)
the pros
· This technique is as sensitive as flow crossmatching and provides the specificity of the antibody.
· One advantage Luminex testing has over other forms of crossmatching is the removal of false positives because of antibody binding to non-HLA antigens.
· Confusion regarding the class of HLA they are binding to is eliminated.
The cons
Luminex testing has some limitations including:
· VXM is less predictive for CDCXM because the latter measures complement-dependent cytotoxic function. VXM predictability is better for positive/negative FLXM than for positive/negative CDCXM results to evaluate a single HLA-A, B, -DR DSA.
· Possible interference of the assay by IgM.
· Incomplete antigen representation on bead sets.
· Variation in HLA density on beads.
References
1. Bielmann D, Honger G, Lutz D, Mihatsch MJ, Steiger J, Schaub S. Pretransplant risk assessment in renal allograft recipients using virtual crossmatching. Am. J. Transplant. 2007; 7 (3): 626.Review Article
2. WILLIAM R MULLEYand JOHN KANELLIS1Understanding crossmatch testing in organ transplantation: A case-based guide for the general nephrologist Nephrology 16 (2011) 125–133
I appreciate that incomplete representation on bead sets is a pitfall
What information do you need to know to support your decision?
I need to know the primary disease of the recipient that lead to ESRD, previous history of sensitization like multiple pregnancies blood transfusion, and previous KTX
Any historic or previous positive crossmatch
Will you accept this offer and go ahead with the transplantation?
We need to do virtual crossmatch, Acceptable time frames for sera used for virtual crossmatches<30 days for sensitized patients and >30 days for unsensitized patients). as the conventional physical crossmatch like CDCXM and FCXM is not possible and needs the mixing of patient sera with donor cells and this will prolong the cold ischemia time and increase the risk of IRI and DGF while the VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a potential crossmatch strategy, VXM by principle used shorter wait times and better outcomes for sensitized transplant recipients The speed of results produced allows a VXM to be performed at the time of donor identification. If no previous history of sensitization, no previous positive crossmatch, and no DSA yes will consider her for TX
What is meant by virtual crossmatch? What are the pros and cons?
VXM may be applied for both sensitized and non-sensitized patients. immune compatibility is assessed by
analyzing the results of donor HLA typing and patient antibodies against HLA. Application of VXM is possible both at the time of
organ allocation and after organ allocation. At organ allocation, the process of listing unacceptable antigens by CPRA % or acceptable mismatches for a given patient and organ allocation based on that listing is equivalent to a negative VXM result. The antibody profile is used for predicting compatibility with prospective donors.
Implementation of the VXM-based approach has resulted in a statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes.
False positive results of VXM may arise where there are significantly low titer and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors
(1). The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.[VXM does not identify the HLA “Null” alleles. (1).More cost with VXM
References
1. Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348. doi: 10.5500/wjt.v7.i6.339. PMID: 29312863; PMCID: PMC5743871.
2. Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
What information do you need to know to support your decision?
I need to know the primary disease of the recipient that lead to ESRD, previous history of sensitization like multiple pregnancies blood transfusion, and previous KTX
Any historic or previous positive physical crossmatch, the CPRA %
Will you accept this offer and go ahead with the transplantation?
We need to do virtual crossmatch as the conventional physical crossmatch like CDCXM and FCXM are not possible as we need the mixing of patient sera with donor cells and this will prolong the cold ischemia time and increase the risk of IRI and DGF while the VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a potential crossmatch strategy, VXM by principle used shorter wait times and better outcomes for sensitized transplant recipients The speed of results produced allows a VXM to be performed at the time of donor identification.
What is meant by virtual crossmatch? What are the pros and cons?
VXM may be applied for both sensitized and non-sensitized patients. immune compatibility is assessed by
analyzing the results of donor HLA typing and patient antibodies against HLA. Application of VXM is possible both at the time of
organ allocation and after organ allocation. At organ allocation, the process of listing unacceptable antigens by CPRA % or acceptable mismatches for a given patient and organ allocation based on that listing is equivalent to a negative VXM result. The antibody profile is used for predicting compatibility with prospective donors.
Implementation of the VXM-based approach has resulted in a statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes.
False positive results of VXM may arise where there are significantly low titer and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors (1). The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.VXM does not identify the HLA “Null” alleles. (1) and its more expensive assay compared to conventional crossmatch.
References
1. Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348. doi: 10.5500/wjt.v7.i6.339. PMID: 29312863; PMCID: PMC5743871.
2 Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
Even though more expansive test, overall costs and shortened time for transplant makes it more economical
1. 1. Choose the correct answer regarding Null HLA alleles
A. It could be missed on VXM
B. It is unexpressed HLA but identified by molecular testing
C. More important in renal transplantation
D. DSA against unidentified null alleles can cause an immunological challenge
E. All the above
Answer: ABD
A VXM does not identify ‘null alleles’, which have DNA sequences identifiable on molecular typing but do not express HLA on the cell surface. In such a scenario, the donor null allele can be identified as a fully expressed product by the recipient, and DSA can develop in the recipient leading to difficulties in future transplantation. It will have no effect if the recipient expresses the antigen.
2. Choose the correct answer regarding VXM
A. Needs regular monitoring of the DSA profile of potential recipients on the waiting list
B. Needs full HLA A, HLA B and DR typing ONLY
C. Is more expensive than wet crossmatch
D. Needs sensitisation history (pregnancy, blood transfusion, etc.)
E. All the above
Answer: AD
NB
I have collected the explanation of the answers from Amit Sharma and Sherif Yousef’s replies
Thank you
Thanks so much; dear our Prof.
Sorry, I worried to choose more than one answer,I choose the most one correct for me
Bcz. Q. (Chose the correct answer)
There are many shades of grey, Dr Mohamed
Thanks alot Prof.Halawa
thank you
thanks, prof Ahmed Halwa
Nice elaboration Prof. Mnay Thanks
Thank you
Thanks Dr Ahmed
◇ What information do you need to know to support your decision?
▪︎ I need to know blood grouping and if there is any history of sensitization (pregnancies, previous transplant or blood transfusions).
◇ Will you accept this offer and go a head with the transplantation?
▪︎If there is no risk I will accept it, because the HLA mismatches is good and the DSA is negative, so this carry low immunological risk.
◇ What is meant by virtual crossmatch? ▪︎Virtual Crossmatch is the process of assessing the results of solid phase and cell based HLA antibody identification assays to predict, or correlate to, the results of a physical crossmatch.
▪︎Based on this data review, donor organ offers can be accepted or declined based on the predicted risk of transplant.
▪︎Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory test (patient anti-HLA antibody and donor HLA typing).
▪︎The goal of VXM is pretransplant risk stratification (1).
◇ What are the pros and cons of virtual crossmatch:
¤ Pros:
1. It can permit import of organs from outside the local organ procurement area for very highly sensitized kidney recipients when a physical crossmatch is not performed prior to transplant (1).
2. VXM may be applied at different scenarios—both for sensitized and nonsensitized patients.
3. Implementation of VXM-based approach has resulted in statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes.
4. The solid-phase assays, including ELISA or multiple beads–based technology (Luminex) can allow an accurate detection and characterization of preexisting anti-HLA antibodies .
5. It decreases the workload in HLA-laboratories and facilitates the organ allocation even in sensitized recipients.
6. the virtual crossmatch does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient (2).
7. It is a safe and efficient way of selecting kidney transplant recipients.
8. It reduces the time kidneys were kept on ice while awaiting identification of a suitable recipient,improved scheduling for surgeons and operating room staff, and alleviated emotional and logistical stress on patients who were called to the hospital only to be sent home hours later after a more suitable recipient was identified (3).
9. VXM using epitope analysis has the advantage of information from high-resolution HLA typing and the LSAB assay and can determine the donor epitope-specific antibody (eDSA) (4).
¤ Cons:
1. Unlike the donor cells used in the PXM, which contains the complete donor HLA repertoire, the LSAB assay usually contains only about 100 HLA alleles for each class, resulting in missing information for certain alleles, especially for common alleles that occur non-western populations.
2. A special labaoratorues which use solid-phase single antigen bead (SAB) technology are not available.
3. The presence of sDSA may be overestimated(4).
4. Because of the high sensitivity of the techniques and because of different current principles that are used in different laboratories to assess the presence of cytotoxic antibodies, some concerns have been expressed related to the ability to predict “true positive” crossmatches in the clinical scenarios. Several studies investigated the predictive value of the virtual-XM and conflicting results have been achieved. At the moment there are no consensus protocols available (5).
________________________
References:
(1)Bhaskaran, Sebastiaan Heidt, et al. Principles of Virtual Crossmatch Testing for Kidney Transplantation. C. Reports, 2022,. 1179-1188
(2) modern era Anna B. Morris, et al. Out with the old, in with the new: Virtual versus physical crossmatching.
(3) Virtual crossmatching improves quality of life for kidney transplant patients.
(4)Bo Peng, Quan Zhuang, et al. Comparison of Physical Crossmatch and Virtual Crossmatch to Identify Preexisting Donor-Specific Human Leukocyte Antigen (HLA) Antibodies and Outcome Following Kidney Transplantation.
(5) Moise A, Baston et al. Challenges and Clinical Significance of Virtual Crossmatch in Kidney Transplantation: Our Experience. SM J Urol. 2017; 3(3): 1032.
I like your reply. However, you need to type headings and sub-headings in bold or underline to make it easier to read.
Ok, thanks Prof Ajay
What information do you need to know to support your decision?
The current status of the donor needs to be known … the hemodynamic condition, amount of blood loss from the accident (if any), biochemical parameters and urine output (within the ICU). In addition, we need to know the blood group of both the donor and the recipient as well as the presence of any active infections.
Will you accept this offer and go ahead with the transplantation?
Yes, we may proceed with the transplantation if there are no absolute contraindications. There is 000 mismatch and there is no DSA – the chance of rejection is low. We also need to ensure that the primary disease of the recipient is controlled – so that the graft does not fall victim to the systemic insults that has been damaging the native kidneys of the patient.
What is meant by virtual crossmatch? What are the pros and cons?
Unlike a physical crossmatch or PXM, a virtual crossmatch or VXM involves comparing and matching (on pen and paper or computer software) between the HLA Antigens of the donor and the HLA Antibodies of the recipient to analyse whether they may cross-react if this donor kidney is transplanted to this recipient.
PROs
CONs
Reference:
Jaramillo, Andrés PhD1; Reddy, K. Sudhakar MBBS2; Heilman, Raymond L. MD3. Using the Virtual Crossmatch to Allow for Safer and More Efficient Kidney Transplantation of Highly Sensitized Patients. Transplantation 104(6):p 1121-1122, June 2020. | DOI: 10.1097/TP.0000000000002925
Yes, co-ordination between lab and clinicians is the key to discuss potential false + and false -.
What information do you need to know to support your decision?
Information needed to support the decision includes:
Donor: Type (Deceased or living), blood group, HLA typing, viral serology.
Recipient: Blood group, HLA typing, history of sensitizing events between after the most recent antibody screening recent (within last 3-6 months) c-PRA and DSAs, extensive pre-transplant work-up.
Crossmatch: either physical (CDC, or flow-cytometry) or virtual cross match. In this clinical scenario, there was no tissue from the donor (like LNs or Spleen). So virtual cross match is the available option.
Will you accept this offer and go ahead with the transplantation?
I will accept this offer.
This is a low immunological offer with 000 mismatch, no DSAs, no medical history in the donor with excellent renal function.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual cross match is performed via a computer system without doing an actual crossmatch, however it requires complete HLA typing of the donor and the recipient in addition to recipient’ s anti-HLA antibodies by solid phase assay method. Antibodies against donor’s antigens will be considered as positive virtual cross match.
Unsuitable donors can be excluded if the recipients have antibodies to their antigens.
Pros:
No need for viable donor cell
Quick procedure.
Reduces cold ischaemia time.
Highly Accurate. Less expensive.
Cons:
False positive results can happen because of presence of non-complement binding antibodies.
Denatured HLA on SAB can lead to false positive results.
False negative VCM can happen with incomplete donor’s HLA typing and with recipient’s DSAs against HLA epitope that was not available on SAB panel.
Reference:
Uptodate.
Sánchez-Fructuoso AI, Marques M, Prats D, et al. Victims of cardiac arrest occurring outside the hospital: a source of transplantable kidneys. Ann Intern Med 2006; 145:157.
Amico P, Honger G, Steiger J, Schaub S (2009) Utility of the virtual crossmatch in solid organ transplantation. Curr Opin Organ Transplant 14: 656–661.
Yes, co-ordination between lab and clinicians is the key to discuss potential false + and false -.
1- Information required:
ABO compatibility
2- As long as there is available HLA typing of the donor and solid phase assay of recipient anti- HLA antibodies with confirmed ABO compatiibility, we can accept the donor (virtual cross match)
3- virtual cross match:
means depending on comparing the available donor HLA typing and the solid phase assay of the recipient anti-HLA antibodies without the need to use the patient serum and the donor lymphocyte for cross match.
Pros:
Cons:
References
Handbook of kidney transplantation 6th edition.
Yes, co-ordination between lab and clinicians is the key
what information are needed:
1. ABO compatibility.
2. Results of receipient HLA antibodies done by single antigen bead assay( SAB)_ Luminx. It should include all results and importantly the recent should be within 3- 6 months. This will allow performing virtual cross match since no samples are available to go for actual cross match.
3. If any sensitization event that occurs after the last results of antibodies( 3- 6 months).
2. Will you go with the Tx?
yes will go with the transplant, since the important clincally mismatches are 0 0 0 and there are no DSA. But important to make sure no further sensitization event after the last results of virtual cross match.
3.what is virtual VXM?
it doesn’t involve the mixing of receipient serum with donor lymphocytes. It involves utilising the donor HLA typing and solid phase assay results of receipient (specific and sensitive) to predict what could be the result of actual cross match.
Advantages:
VXM is best utilized in deceased organ transplants as it can decrease the waiting times in the list by identifying donors especially for those who are sensitised. It is quick and can be performed at the time of deceased donor availability and especially used when historical serum samples for actual cross match are not available in less than 6 months.
Disadvantages:
A. False positive results when titre of antibodies are low ( as SPA is very sensitive) or the antibodies are not complement dependent. False positive results lead to incorrect exclusion of potential donors.
B. False negative results when HLA ag are classified differently and this incorrectly represented.
C. VXM doesn’t detect Null alleles.Null alleles are alleles identified by DNA sequencing when using molecular typing to identify HLA Ag. They are not expressed as products on cell surface. When null alleles are not detected as in VXM it means that transplant is done with the donor having the non detected alles as this can lead to the developement of DSA in the future. This doesn’t carry the risk of humoral rejection and is well tolerated but can affect future transplant. Worth noticing that the effect of null alles is less marked in solid organ transplant than stem cell transplant .
Yes, co-ordination between lab and clinicians is the key to discuss potential falacies.
PLease type headings in bold or underline
I like your decision making, but there are spelling errors.
1. A 41-year-old CKD 5 female received a deceased kidney offer, 000 mismatch. There is no DSA. The donor was 34-year-old, died in a road traffic accident. No past medical history with excellent kidney function. There was no blood sample or lymphoid tissues available to run the crossmatch.
What information do you need to know to support your decision?
– ABO compatibility
– HLA typing
– Virtual crossmatching
– viral serology/ status for both donor and recipient i.e., CMV, EBV, HIV, hepatitis B, hepatitis C
– history of prior senstisation i.e., blood transfusion, pregnancy, previous transplant
– history of prior infections (e.g., tuberculosis) and malignancies
– cause of CKD in the recipient
– any personal or family history of diabetes, hypertension, kidney disease in the recipient
– donor type i.e., DBD, DCD
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept the offer and proceed with transplantation given the 000 mismatch, no DSA, excellent kidney function, young donor with no significant past medical history
What is meant by virtual crossmatch? What are the pros and cons?
A crossmatch test helps determine the immunologic risk of a transplant recipient against a potential donor.
It ensures that there are no circulating antibodies in the recipient that are directed against the donor antigens.
There are different types of crossmatch tests: –
· Physical crossmatch test (PXM)
· Virtual crossmatch (VXM)
Physical crossmatch test (PXM) (1)
e.g., complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FCXM)
They require mixing of the recipient’s serum and the donor cells hence are labor intensive and pose a logistics challenge.
Virtual crossmatch (VXM) (1-3)
It assesses the immunologic compatibility between the recipient and potential donor by analysing the results two physical laboratory tests done independently i.e., recipient anti-HLA antibody and donor HLA typing
It involves use of: –
· solid phase assays to detect circulating antibodies in the recipient directed against individual HLA
· DNA-based methods to type donor HLA specificities at a higher resolution
Pros of virtual crossmatch (4)
– Increased sensitivity/ ability to detect donor-specific HLA antibodies
– Improves transplantation access for highly sensitized patients
– Improves risk assessment for transplant rejection
– Can be performed with stored serum hence shortening the cold ischemia time
Cons of virtual crossmatch (4)
– Requires more coordination between the immunology lab and the transplant team members
– Denatured HLAs on single antigen beads may lead to false positive results
– The antibody profile can change with time
References
1. Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney international reports. 2022 Jun;7(6):1179-88. PubMed PMID: 35685330. Pubmed Central PMCID: PMC9171621. Epub 2022/06/11. eng.
2. Morris AB, Sullivan HC, Krummey SM, Gebel HM, Bray RA. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era. Hla. 2019 Dec;94(6):471-81. PubMed PMID: 31515937. Pubmed Central PMCID: PMC7341023. Epub 2019/09/14. eng.
3. Bray RA, Nolen JD, Larsen C, Pearson T, Newell KA, Kokko K, et al. Transplanting the highly sensitized patient: The emory algorithm. American journal of transplantation : official journal of the American Society of Transplantation and the American Society of Transplant Surgeons. 2006 Oct;6(10):2307-15. PubMed PMID: 16939516. Epub 2006/08/31. eng.
4. Callus R, Buttigieg J, Anastasi AA, Halawa A. Basic concepts in kidney transplant immunology. British journal of hospital medicine (London, England : 2005). 2017 Jan 2;78(1):32-7. PubMed PMID: 28067566. Epub 2017/01/10. eng.
Yes, co-ordination between lab and clinicians is the key to discuss potential pitfalls
·What information do you need to know to support your decision?
=============================
·Will you accept this offer and go ahead with the transplantation?
=============================
·What is meant by virtual crossmatch? What are the pros and cons?
Challenges in the Routine Implementation of VXM Testing:
References
I am sorry for resending, by mistake, the same contribution.
Repeated in error as is down below
Chose the correct answer regarding VXM
A. Needs regular monitoring of the DSA profile of potential recipients on the waiting list
B. Needs full HLA A, HLA B and DR typing ONLY
C. Is more expensive than wet crossmatch
D. Needs sensitisation history (pregnancy, blood transfusion, etc.)
E. All the above
-D
A, C, D
A &D
A. TRUE: VXM integrates the donor’s molecular HLA typing with the recipient’s comprehensive antibody profile.
B. FALSE: In contrast to a PXM, the VXM does not require viable donor cells but rather relies on complete HLA typing of the donor & current antibody assessment of the recipient.
C. FALSE: VXM may be the only pretransplant “crossmatch” necessary. It reduces unnecessary crossmatching & increases the likelihood of finding crossmatch-compatible donors for highly reactive patients.
D. FALSE
E. FALSE
D
E
Hmmm, there are so many variations from truth here.
A-D
A& D
A. Needs regular monitoring of the DSA profile of potential recipients on the waiting list
B. Needs full HLA A, HLA B and DR typing ONLY
C. Is more expensive than wet crossmatch
D. Needs sensitisation history (pregnancy, blood transfusion, etc.)
E. All the above
A and D
Choose the correct answer regarding VXM
A. Needs regular monitoring of the DSA profile of potential recipients on the waiting list. (True)
B. Needs full HLA A, HLA B and DR typing ONLY. (false)
C. Is more expensive than wet crossmatch. True
D. Needs sensitization history (pregnancy, blood transfusion, etc.). True
E. All the above False
A: True. DSA profile should be done at least once in 3 months to get more accurate results of VXM
B. False. It is better to get full HLA typing as the DSA prifle will include antibodies against HLA other than A, B and DR also.
C True. Although VXM does not require any physical testing (just comparison of HLA typing of the donor with DSA profile of the recipient) the testing for HLA typing of the donor is costlier than the cost of wet crossmatch (assuming that the DSA profile was done historically).
D. False. Sensitization history is not relevant except if the sensitization event has taken place after the last DSA profile testing.
E. False
A: True. DSA profile should be done at least once in 3 months to get more accurate results of VXM
B. False. It is better to get full HLA typing as the DSA prifle will include antibodies against HLA other than A, B and DR also.
C False. VXM does not require any physical testing (just comparison of HLA typing of the donor with DSA profile of the recipient) , hence it does not cost anything while a wet crossmatch is a physical test which would require expenditure.
D. True. Sensitization history relevant if the sensitization event has taken place after the last DSA profile testing. A wet crossmatch should be done in the event of a history of sensitization.
E. False
A. is the best we should monitor DSA complete profile Q 3 month for all waiting list DD KTx
A- True
as initiation of a virtual cross match protocol using solid phase histocompatibility techniques has significantly increased the access of sensitised patients ( prior transplant, pregnancy or blood transfusion history) for kidney transplant.
B- False
C-True ( more cost effective).
D- True.
E-False.
Regarding VXM
A. Regular monitoring of the DSA profile of potential recipients is needed (True) if there is a history blood transfusion or pregnancy.
B. Needs full HLA A, HLA B and DR typing (False) as well as HLA C, and HLA DQ typing.
C. Is more expensive than wet crossmatch (True) because HLA typing of all antigens of the donor and recipient’s anti-HLA antibody profile by SAB technology are expensive.
D. Sensitisation history (pregnancy, blood transfusion) (True) is necessary to ensure the validity of the VXM.
E. All the above (False)
A,C and D
A,C& D
Answers:
A- True
B- False
C- False
D- True
E- False
A, D
A and D
A and D
A =T
B =F
C =F
D =T
A&D
A,D
B
A,D
A, C and D are true
A,C,D
A ,C , D ,ARE THE CORRECT ANSWERS
A , D
A & D
Answers:
A- True
B- False
C- False
D- True
E- False
_⭐⭐correct answer is A and D.
_Virtual cross match is done in deceased donor transplantation.
_it needs HLA typing of the donor and DSA in the recipient (by luminex single Ag bead).
_ It is easier and less expensive than wet cross match. However, frequent monitoring of DSA is required every 3 months.
A
A
D
I am not sure about the cost factor
A& D are correct.
A, D are correct.
A and D are correct answers.
A,D
Chose the correct answer regarding Null HLA alleles
A. It could be missed on VXM
B. It is unexpressed HLA but identified by molecular testing
C. More important in renal transplantation
D. DSA against unidentified null alleles can cause an immunological challenge
E. All the above
Correct answers are:
A, B. & D
-D
A,B, D
A, B &D
A. Missed on VXM
B. Produce no serologically detectable products
C. More important in stem cell transplant
D. Yes can cause immunological challenge
A- YES MISSED ON VXM
C- YES There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation.
D- YES VXM does not identify the HLA “Null” alleles.
====================================================================
B- FALSE the null allele is misidentified as a fully expressed product and, therefore, transplanted with a donor bearing the expressed antigen.
D
A-B-D
A. It could be missed on VXM
B. It is unexpressed HLA but identified by molecular testing
C. More important in renal transplantation
D. DSA against unidentified null alleles can cause an immunological challenge
E. All the above
A,B and D
A. True.
B. True.
C. False. More important in stem cell transplant.
D. True.
E. False.
A,B, D are correct
C=> the risk of null alleles is misleading for its fully expressed in stem transplantation, however, the risk is lower in solid organ transplantation which leads to DSA formation but has no life threaten effect.
A- True.
as Null HLA alleles are non-functional alleles caused by genetic mutations could be missed by VXM and serological typing is recommended.
B- True.
C- False
has significant role in hematopoietic stem cell transplantation.
D-False
as Null HLA alleles produce no detectable antigens on the cell surface and can be recognised through a comparative examination of serological and DNA-typing or through family study.
E-False.
A,B AND D
Regarding Null HLA alleles
A. (TRUE) It could be missed on VXM if the HLA Typing not done via molecular sequencing. False representation of a donor’s null allele as an expressed allele will unfortunately prevent transplantation of a possible donor kidney with no antigens for that allele into a patient even if that recipient has anti-bodies to that antigen.
B. (TRUE) It is unexpressed HLA but identified by molecular testing. Null alleles are not found on serologic testing.
C. (FALSE) More important in renal transplantation. Actually it is only important in the special case where the null HLA allele is present in the recipient and the same HLA antigen is expressed on the donor kidney resulting in DSAs and rejection.
D. (TRUE) DSA against unidentified null alleles can cause an immunological challenge. DSAs against expressed antigens of donor alleles by the recipient carrying non-expressing null alleles for the same HLA antigens can cause rejection and need plasmapheresis or other anti-rejection therapy.
E. (FALSE) All the above
A, B & D
Answers:
A- True
B- True
C- False
D- True
E- False
A ,B, D
A, B and D
A B and D
A & D
1/sequencing-based typing was deemed the best technique in reducing problems with ambiguities and null alleles.
2/ it can cause GVHD in stem cell transplant. less important in renal transplant
I agree
A – T
B -T
C -F
D -T
A, B&D
A,B,D
A,B,D
A, B and D are true
Ans;
A , B , D
A, B & D
A. True.
B. True.
C. False. May be important in stem cell transplant.
D. True.
E. False.
⭐ ⭐ correct answer is A, B and D
_Null HLA alleles are not expressed on cell surface, so can be missed in virtual cross match. However it can induce DSA that can cause immunological challenge
A
B
D
A,B,D are correct.
A, B and D are correct.
·What information do you need to know to support your decision?
=============================
·Will you accept this offer and go ahead with the transplantation?
=============================
·What is meant by virtual crossmatch? What are the pros and cons?
Challenges in the Routine Implementation of VXM Testing:
References
Madhu C. Bhaskaran, Sebastiaan Heidt and Thangamani Muthukumar, Principles of Virtual Crossmatch Testing
for Kidney Transplantation, Kidney Int Rep (2022) 7, 1179–1188; https://doi.org/10.1016/j.ekir.2022.03.006
Yes, co-ordination between lab and clinicians is the key appreciating inter-lab variations.
A 41-year-old CKD 5 female received a deceased kidney offer, 000 mismatch. There is no DSA. The donor was 34-year-old, died in a road traffic accident. No past medical history with excellent kidney function. There was no blood sample or lymphoid tissues available to run the crossmatch.
1.INFORMATION NEEDED;
-Pairs blood group.
-Hx of any CA and treatment status.
-Hx of any chronic illnesses.
-During postmortem evaluate for any features of a granulomatous disease or lymphadenopathies.
-Any risk of sensitization – blood transfusion, pregnancies of previous transplantation.
-Viral infection screen status- HIV,CMV,EBV etc
2.WILL YOU ACCEPT THE DONOR AND PROCEED WITH TRANSPLANTAION?
Yes I will.
Favorable donor- 000 mismatch, No DSA..
A VXM will be done
3.WHAT IS VXM? PROS/CONS ?
VXM is a virtual or non physical analysis of anti HLA antibodies in recipients with donor HLA profile. It has a +VE predictive value of more than 85% and a -VE predictive value of 50%.3monthly collection of sera is done for antibody screening via solid phase assay to ensure the right anti HLA profile at the time of transplantation.
PROS.
-Increased sensitivity.
-Facilitates transplantation of highly sensitized recipients.
-Offers a better risk assessment for rejection.
-Done with stored sera thus decreases cold ischemia time.
-Detection of both acceptable and non acceptable AGs decreases shipping time of organs, less SX delays and also decreases the cold ischemic time.
CONS.
-Denatured HLA antigens on SAB and presence of null antigens may lead to false +VEs
-Needs better coordination between lab and transplant team.
-False negative results can be from ;Incomplete typing of donor, DSA in recipient sera from HLA epitopes not on SAB panel.
REF;
Ahmed Halawa et al ; Basic concepts of kidney transplant immunology’VL 78,10.12968/hmed.2017.78.1.32.British Journal of Hospital Medicine.
Yes, co-ordination between lab and clinicians is the key to discuss potential false + and false -.
Thank you.
What information do you need to know to support your decision?
1- ABO Compatibility
2- V – XM Should always be done (blood from recipient for HLA typing)
3-HLA typing for recipient for sure
4– Luminex- SAB (single antigen bead testing ) for Anti-HLA Ab.
5- Flow XM (T and B Lymphocytes)
6-History of sensitization especially after last blood sample given by recipient
7- Virological screening : CMV, EBV, VZV , HBV,HCV, HIV
8- Any history of active infections/ malignancy in the donor.
Will you accept this offer and go ahead with the transplantation?
Because of Young Donor and (000 HLA MM ), Excellent kidney function , and absence of DSA ,I will accept this donor depending on the ABO and virtual cross match (VXM)
What is meant by virtual crossmatch? What are the pros and cons?
It is not a true crossmatch but rather comparing the recipient antibody from solid phase testing to the donor HLA typing as a prediction of the actual crossmatch.
Predicts presence of donor specific antibodies using solid phase without an actual crossmatch , compares recipient’s HLA ab to donor HLA type to predict Xmatch results its use in lieu of ‘wet’ crossmatch is on the rise
It required Complete tissue type of the donor (HLA A, B, C, DP, DQ, DR) , Complete tissue type of the recipient , Complete anti HLA antibody analysis of the recipient Requires recent blood: < 3m
What are the pros of VXM :
1-Decreasing Test cost
2- Shortening Cold ischemia time
3- Facilitate kidney paired donation
4- The virtual crossmatch ensures timely allocation of organs and increases the chance of transplantation in highly sensitized individuals.
What are the Cons of VXM :
1-Denatured HLA on single antigen beads may lead to a false positive result.
2-Requires more coordination between immunology lab personnel and transplant team.
3-are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
4-VXM does not identify the HLA “Null” alleles.
False positive:
1- very low titer (it detect Ab with MFI >1000 while actual cross match need MFI >5000 to be +ve)
2- allele specific antibodies (e.g., anti-body to DRB1*0401 but not other DRB1*04 alleles) which may unnecessarily exclude other DR4 donors.
3- identify null alleles that are not expressed as antigens on the cell surface but would be excluded by VXM based on typing alone.
Falsely negative:
-All potential HLA antigens in the population cannot be completely represented on solid phase tests , Care must be taken to ensure that the donor alleles are completely represented on the solid phase panel in order to report a negative VXM
Reference:
1- Basic concepts in kidney transplant immunology British Journal of Hospital Medicine, January 2017, Vol 78, No 1 Dr Roberta Callus, Dr Jesmar Buttigieg, ,Dr Andrei Agius Anastasi, Mr Ahmed Halawa.
2- Tinckam KJ. Basic histocompatibility testing methods. In: Chandraker A, editor. Core concepts in renal transplantation. New York: Springer Science + Business Media, LLC; 2012. pp. 21–42.
3- Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339.
A:
We need to do a virtual cross-match (VXM), using donor HLA typing and solid-phase antibody screening.
Help is to be used at the time of transplantation as in this case and in cases that need to reduce the waiting time of transplantation.
It helps to do a cross-matching in a way other than prospective cross-match, given that flow cytometry is progressively advancing sensitivity and specificity.
B:
We can accept this donor based on his 000 miss-match and no DSA.
C:
VXM; itis good at time transplant cross-match, and it is very sensitive and more specific when using a recent serum sample.
Can give a false positive or a false negative result.
Does not identify an HLA (Null) allele, with a great risk of a non-identifiable allele, although is much lower in SOT.
A false negative result may arise due to the fact that not all HLA antigens are presented correctly.
False positive results may arise when there is an inadequate titer or non-complement binding antibody, resulting in a wrong exclusion of potential donors.
I appreciate your explanation of limitations of VXM
1-HLA typing
2-History of previous sensitization like pregnancy,blood transfusion,previous transplants
3-cross match result
4-DSA titer
5–viral study
I will accept this donor as there is 000 mismatch and no DSA
A virtual crossmatch (VXM) is used to ascertain the presence of HLA antibodies in a transplant recipient’s serum and to determine, virtu- ally, the potential flow cytometric crossmatch (FXM) results with an available donor.
VXM testing is routinely used to aid in the selection of donor kidneys for highly sensitized patients. A VXM can be a valuable tool in helping to minimize cold ischemia time and therefore improve donor organ allocation.
The correlation of the virtual crossmatch with flow cytometry crossmatch is greater than 85% .
It requires HLA typing of the donor and a recent anti-HLA profile of the potential recipient. To ensure a correct anti-HLA profile at the time of the transplant call, regular collection of sera every 3 months is required for antibody screening via solid-phase assays, because antibody titres and specificities can change over time. Any potential sensitizing events like pregnancy, blood transfusions and previous transplantation must be documented accurately.
A false negative virtual crossmatch can arise from
1-Incomplete typing of the donor
2- donorspecific antibodies in the recipient serum against a unique HLA epitope which is not available on the SAB panel, can give rise to a false negative result
not all donor-specific antibodies detected by LuminexSAB are detrimental to graft outcomes. Studies have shown that donor-specific antibodies detected by SAB but with a negative CDC-XM are a major risk factor for early allograft rejection and long-term graft loss
False positives may result from
1-antibodies directed at HLA epitopes that come about secondary to denatured HLA antigens on the SAB
2-the presence of null alleles, which are not expressed as antigens on the cell surface in vivo
advantages
the detection of acceptable and unacceptable antigens This avoids unnecessary shipping of organs resulting in less surgery delays, reduces cold ischaemia time, encourages cost savings and improved transplanting highly sensitized patients. A number of studies have reported low risk for early antibodymediated rejection and good allograft survival even in sensitized patients when using the virtual crossmatch
Disadvantage
Denatured human leucocyte antigens on single antigen beads may lead to a false positive result
Requires more coordination between immunology lab personnel and transplant team
Reference
1-Roberta Callus, Jesmar Buttigieg, Andrei Agius Anastasi, Ahmed Halawa, Basic concepts in kidney transplant immunology. British Journal of Hospital Medicine, January 2017, Vol 78, No 1.
Yes, co-ordination between lab and clinicians is the key
1-What information do you need to know to support your decision?
–ABO compatibility for recipient and donor.
-HLA typing for recipient and donor (CDC , FCXM and cPRA).
-Luminex-SAB (single antigen bead) did not identify any donor specific antibodies (DSA).
-History of sensitization (blood transfusion-prior transplantation).
–As serum or lymphoid tissue are not available to do physical crossmatch like CDC of flow cytometry,Virtual cross-match is possible application.
2-Will you accept this offer and go ahead with the transplantation?
-Yes; I will accept This Deceased Donner for transplantation;
-which is (Young age 34Y-with no past medical history and with excellent kidney function),
-which considered standard immunological risk for renal Transplantation (000 mismatch -No DSA).
3-What is meant by virtual crossmatch? What are the pros and cons?–In virtual crossmatch (VXM), both donor HLA typing and solid phase antibody screening are utilised together. It is not precisely a crossmatch in the sense of mixing serum and lymphocytes.
-The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
-This is particularly important in deceased donor renal transplantation. Quick results mean less cold ischemia times.
-The speed of results generated allows a VXM to be performed at the time of donor identification owing to the fact that there is progressively sensitive and specific flow cytometry technology.
-VXM permits transplant physicians to consider donor organs that would not otherwise be available by means of a prospective crossmatch strategy, and thereby, allows to consider a potentially positive crossmatch a risk factor for donor selection.
-The VXM should, therefore, be done considering all available serum results including at least one recent within less than 3-6 month for a given patient.
-The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
–False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors.
– False negative results of VXM may arise due to the fact that the list of all potential HLA donor antigens have been classed differently and, therefore, can not be correctly represented.
-Furthermore, VXM does not identify the HLA “Null” alleles. Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
-In excess of 190 null alleles have been identified across HLA class I and II.
-There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation.
-References;
–Human leukocyte antigen typing and crossmatch: A comprehensive review;World J Transplant. 2017 Dec 24; 7(6): 339–348.Published online 2017 Dec 24. doi: 10.5500/wjt.v7.i6.339.
-Gupta A, Iveson V, Varagunam M, Bodger S, Sinnott P, Thuraisingham RC. Pretransplant donor-specific antibodies in cytotoxic negative crossmatch kidney transplants: are they relevant? Transplantation. 2008;85:1200–1204.
-Tinckam KJ. Basic histocompatibility testing methods. In: Chandraker A, editor. Core concepts in renal transplantation. New York: Springer Science + Business Media, LLC; 2012. pp. 21–42.
-Gebel HM, Bray RA, Nickerson P. Pre-transplant assessment of donor-reactive, HLA-specific antibodies in renal transplantation: contraindication vs. risk. Am J Transplant. 2003;3:1488–1500.
-Bray RA, Nolen JD, Larsen C, Pearson T, Newell KA, Kokko K, Guasch A, Tso P, Mendel JB, Gebel HM. Transplanting the highly sensitized patient: The emory algorithm. Am J Transplant. 2006;6:2307–2315.
I like your decision-making.
*Blood grouping of both patient and recipient.
*Allo antibodies testing against HLA (A, B,C,DRB1, DRB 3,4,5, DQB1, DQA1, DPB1, DPA1) plus other non-HLA antigens,.,
* Is the recipient have any history of potential sensitization .
*Is the alloantibody testing sample is recent ?? according to the local program determination of the definition of a “recent” sample.
* Is there any agreement between the laboratory and the transplant program which describe the circumstances when a prospective physical crossmatch is required.
*Is the donor typing include HLA and other histocompatibility antigens to which antibodies have been identified in the potential recipient.
* Virology screening of both donor and recipient and other required systemic evaluation of recipient and donor regarding preparation of kidney transplant .
Yes if fulfill the criteria of virtual crossmatching that agreed by laboratory director or a technical supervisor who meet the clinical consultant qualifications and serve in this role.
Virtual crossmatch (VXM)is an assessment of immunologic compatibility based on the patient’s alloantibody profile compared to the donor’s histocompatibility antigens. Based on well defined antigens and antibodies .Antibody presence or absence should be confirmed by more than one method and should be reconfirmed on an on-going basis ¬ Histocompatibility can be defined as encompassing both HLA and non-HLA components.
For non sensitized patients who do not have circulating antibodies, PXM result against any prospective donor can be assumed to be negative ,although VXM is a risk assessment tool and there is currently no consensus on the goal of VXM— whether the risk assessment involves predicting the result of a PXM or the posttransplant outcome.
Prons of VXM:
Potential Benefits of Virtual Crossmatches for the patients,laboratory and transplant program :
For patients :
-It decrease the time needed for evaluation of compatibility (particularly with thoracic transplant patients); results in more efficient use of the system .
¬ Reduced cold ischemia time.
¬ Better matched donor/recipient by Increasing sensitivity and specificity of testing .
¬ Less likely to deny access for a false positive physical crossmatch .
¬ Facilitates matching over larger geographic areas, renal paired donations, and the transplantation of more highly sensitized patients by providing better access to sensitized patients .
¬ Reduced cost and waiting time .
¬ Performance of a physical XM is not precluded and can be completed concurrently with or after transplantation.
¬ It works as a risk assessment for patient desensitization needs.
For the Laboratories:
¬ It allows better coordination and communication with transplant programs.
¬ Improvement of quality management with better patient and transplant program satisfaction.
¬ Increased efficiency, which allows for more focus on patients with problems and results in cost savings.
¬ It helps in decreasing on-call time expenditure by testing personnel.
For the transplant programs:
¬ Reduction of ischemia time .
¬ Improvement of risk assessment for rejection
¬ Improved transplant physician and patient satisfaction by improving access to transplantation for geographically and immunologically disadvantaged candidates .
¬ Reduction of unexpectedly positive physical crossmatches which leads to more efficient use of transplant personnel.
¬ Optimization of immunosuppression and desensitization protocols
¬ Management of transplant related logistics (i.e. OR schedules) will be more flexible .
Cons :
Potential Disadvantages of Virtual Crossmatches for patients laboratory and transplant program :
For patients :
¬ There is potential to deny use of a donor organ that could be successfully transplanted .
¬ Requires patient to receive and understand more complicated information
¬ Negative crossmatch (physical or virtual) does not guarantee compatibility.
For the laboratories :
¬ Potentially more difficult for staff to maintain competency in performing physical crossmatches when they are done less frequently .
¬ Increased unreimbursed interpretation time.
¬ Requires more coordination with the transplant program.
For transplant programs:
¬ Program staff have to learn a new interpretive vocabulary.
¬ Additional time and work to ensure that patients understand their risk and get all the information on time .
¬ No reimbursement for time/effort of professional rendering a virtual crossmatch.
Reference:
1.https://www.cdc.gov/cliac/docs/addenda/cliac1114/8_BRAY_Virtual_Crossmatch_Workgroup_Report_Nov-2014.pdf
2.Principles of Virtual Crossmatch Testing for Kidney Transplantation Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani Muthukumar4,5
3. Pinelli DF, Tambur AR. Virtual crossmatching for deceased donor transplantation: one size does not fit all. Kidney Int.2020;97:659–662. https://doi.org/10.1016/j.kint.2020.02.001
Yes ,team approach is crucial when you say ‘all staff…’.
In the current scenario of full HLA match at HLA-A,B and DR without DSA:I will need for ABO compatibility and virtual cross match to proceed for transplantation.
Will you accept this offer and go ahead with the transplantation?
If there is no ABO incompatibility and negative VXM ,I will proceed directly for transplantation.
In the same time according to information available with full HLA match and no DSA ,we can proceed even without VXM.
What is meant by virtual crossmatch? What are the pros and cons?
Generally speaking ,The main target for cross match techniques is to identify the recipients who have anti HLA antibodies against a specific donor (Donor specific antibodies) and they have a higher chance for hyperacute rejection as result of the presence preformed antibodies. DSAs are commonly generated by previous transplantation, frequent blood transfusion and pregnancy.
The virtual crossmatch: The Wait Is Over
The Physical crossmatching is costly and time consuming.
This technique is based on the comparison between donor and recipients without requiring viable donor cells, depending on complete HLA typing of the donor and anti-HLA antibodies of the recipient. The use of the virtual crossmatch as a final decision to proceed with transplant across transplant centres can lead to decreased cold ischemia time and lower DGF rates without increased risk of rejection. These cross match results must be updated every 3 months especially in patients on cadaveric transplant list.
Titres, specificities, and presence or absence of antibodies could be changed by time.So the use of antibody specificity from historical serum sample (older than 6 months) could not predict a crossmatch with certainty. As well as Other factors that can influence antibody specificities should be considered, which include pregnancies, transplants and blood transfusions.
Cons of VXM:
-False positive results of VXM when there is significantly low titre and/or non-complement binding antibodies,that can leads to wrong exclusion of potential donors.
-False negative results of VXM due to the fact that the list of all potential HLA donor antigens have been classed differently and can not be correctly represented. The results from VXM are not 100% accurate and current practice mandates a physical crossmatch be performed as well.
I appreciate your explanation of limitations of VXM
What information do you need to know to support your decision?
—————————————————————————————-
1-The ABO compatibility.
2-Hisory of ;
a-DM ,hypertension and renal disease .
b-Chronic or recent active infection .
c-malignancy
d- risk for transmissible disease (viral infection )
Will you accept this offer and go ahead with the transplantation?
—————————————————————————–
With 000 HlA mismatches ,excellent kidney function ,compatible blood group and absence of DSA ,I will accept this donor depending on the virtual cross match .
What is meant by virtual crossmatch? What are the pros and cons?
———————————————————————————————
Compare the recipient anti HLA Abs and the donor HLA profile .Detects acceptable and unacceptable Ag.
Advantages of virtual cross match ;
——————————————————-
1- The virtual crossmatch ensures timely allocation of organs and increases the chance of transplantation in highly sensitized individuals.
2- May be performed with stored sera therefore shortening cold
ischaemia time.
3-Increased sensitivity.
Disadvantages of virtual cross match ;
——————————————————
1-Denatured human leucocyte antigens on single antigen beads may lead to a false positive result.
2-Requires more coordination between immunology lab personnel and transplant team.
Reference ;
———————
1- Basic concepts in kidney transplant immunology British Journal of Hospital Medicine, January 2017, Vol 78, No 1 Dr Roberta Callus, Dr Jesmar Buttigieg, ,Dr Andrei Agius Anastasi, Mr Ahmed Halawa.
Disadvantages of virtual cross match ;
————————————————–
3-are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well.
4-VXM does not identify the HLA “Null” alleles.
Yes, hence VXM is always followed by wet X match electively on next working day.
When a cadaveric organ is offered for transplant, certain information is required before proceeding with the transplant. It includes:
a) Blood group compatibility of the donor and recipient.
b) Human leukocyte antigen (HLA) mismatch using HLA typing of the donor and recipient.
c) Assessment for presence of donor specific antibodies (DSA) in the recipient using a solid phase assay like Luminex which should not be very old (preferably done in last 3 months).
d) Virological screening including human immunodeficiency virus (HIV), hepatitis B and Hepatitis C viral infection, cytomegalovirus (CMV), Epstein Barr virus (EBV)
e) Any history of active infections/ malignancy in the donor.
Yes. This recipient-donor pair has a 000 mismatch, with no DSA. Assuming that the blood group compatibility has been checked prior to the offer, even in absence of a crossmatch, due to negative virtual cross match (000 mismatch and no DSA), the offer is acceptable.
A virtual crossmatch (VXM) involves matching a pair of recipient and donor utilizing the HLA typing of the donor and the presence of antibodies in the recipient serum, which is done using a solid phase assay on a historical serum of the patient (1). There is no physical mixing of recipient serum with the donor lymphocytes.
The pros of VXM include: Shorter time to transplantation and cold ischemia time (it can be done even at the time of organ retrieval itself), increase chances of finding crossmatch negative donors for sensitized patients (by matching prior to physical crossmatch itself) (2).
The cons of VXM include: The VXM depends on the anti-HLA antibodies in the recipient. If the solid phase assay results for the anti-HLA antibodies was done more than 3 months back, or if there is history of sensitization after the last solid phase assay, then VXM cannot be relied upon. Also, presence of non-complement binding antibodies, or low-titre antibodies may lead to a false positive VXM, preventing a transplant (3). A false negative VXM can be due to misclassification of donor HLA antigens. A VXM does not identify ‘null alleles’, which have DNA sequences identifiable on molecular typing but do not express HLA on cell surface (1). In such a scenario, donor null allele can be identified as a fully expressed product by the recipient, and DSA can develop in the recipient if the expressed antigen is not present in the recipient, leading to difficulties in future transplantation. Additionally, if the donor HLA type is not present in the solid phase assay testing kit, then the antibodies against those HLA antigens could have been missed, hence VXM cannot be used in such a scenario (3).
References:
Excellent answer, well done Amit
What information do you need to know What is meant by
virtual crossmatch? What are the pros and cons?to support your decision?
We need to know
*Blood group of both donor and recipient
*HLA typing .
*past medical history of the donor.
*cause of kidney disease if the recipient.
*history of sensitization, Blood transfusion, pregnancy, previous transplant.
*Virology and chronic infections as CMV, EBV, Hbv ,HIV and TB.
* as there are no blood or lymph samples are available Virtual cross matching must be done recent before transplantation.
Will you accept this offer and go ahead with the
transplantation?
This is a good offer as there is no DSA and there is 000 mismatch, in absence of any other contraindications from history i will accept this donor
What is meant by virtual crossmatch? What are
the pros and cons?
American Society for Histocompatibility and
Immunogenetics defines VXM test as an assessment of immunologic compatibility
based on patient’s alloantibody profile compared with donor’s
histo-compatibility antigens.
The VXM
test uses the results of 2 independently done physical laboratory tests and
does not involve mixing of serum and cells.
Several transplant centres have reported their success with proceeding to transplant
based on VXM results and eliminating pre transplant PXM to reduce cold ischemia time in deceased kidney
donors.
The goal of VXM is pre transplant risk stratification— though there is no consensus on
whether such risk assessment involves predicting the PXM result or the post transplant
outcome.
Pros:
-Reduce cold ischemia time in deceased kidney donors
-Detect the unacceptable antigens
-VXM is more sensitive than PXM.
Cons:
– False positive results of VXM by detection of insignificant Ab
– Also detection of non-complement
binding AB that may miss a good offer and increase waiting time.
Technical issues related to the assay and a low threshold for calling an antibody as
present (over-calling) could result in a false-positive DSA result.
False negative results also may present as MFI cutoff values are different between labs.
-SAB manufacturing issues result in lot-to-lot
variability
-SAB assay use synthetic HLA on beads as the target and may not reflect the cellular profile—for example, cell
surface expression of HLA-C is lower than HLA-A and -B, but this is not reflected on the beads.
Reference:
Madhu C.
Bhaskaran, Sebastiaan Heidt.Principles of Virtual Crossmatch Testing for Kidney
Transplantation .kidney Int Rep (2022) 7, 1179–1188.
I like your decision-making.
What information do you need to know to support your decision?
I will need the following information:
* For both the donor and the recipient: Blood group, HLA typing with virtual cross match, viral serology including CMV and EBV.
* For the recipient I need to know the primary cause of renal failure, sensitization history which includes history of previous transplant, pregnancy or blood transfusion and previous DSA tests and when the patient had last SAB test ?
* For the donor, I need to know the warm ischemia time, type of deceased donor (DCD vs. DBD)
Will you accept this offer and go ahead with the transplantation?
I will accept this offer with 000 mismatch and no DSA, excellent graft function for previously healthy young donor.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch (VXM) assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing. The goal is only for pretransplant risk stratification and there is no consensus that will predict the result of physical crossmatch PXM or the outcome of the transplantation.
The pros of VXM includes increased sensitivity, can be performed in shorter time and decrease the cold ischemia time, improve access to the transplantation for highly sensitized patients and can improve this risk assessment for graft rejection.
The cons of VXM includes the false positive results which can occur due to denatured HLA or SAB. The usage of historical serum sample in VXM can result in false negative test as presence of antibodies can vary significantly overtime. VXM requires more coordination between immunology lab and personnel and transplant team. For that, the results of VXM are not always accurate and PXM is still mandatory in most cases.
I like your decision-making.
VXM is always followed by wet X match electively on next working day.
· ABO blood group
· Recent HLA antibody testing of recipients (3-6 m)
· complete HLA typing of donor
· History of previous sensitization (pregnancies, transplants and blood transfusions.)
· Infectious risk for (CMV/EBV)
If virtual cross match negative for class I/II I can proceed
Virtual crossmatch
both donor HLA typing and solid phase antibody screening are used together. by “mixing” identified antibody specificities of recipient serum with donor HLA antigens
Pros
· shorter wait times
· improving organ allocation system
· less costs
· shorter cold ischemia time
· rapid result
· facilitating kidney paired donation programs
· we can consider donors that would not be available by means of physical crossmatch strategy,
cons
so The results from VXM are not a hundred percent accurate
I like your decision-making.
VXM is always followed by wet X match electively on next working day.
History
====================================================================
What information do you need to know to support your decision?
====================================================================
Will you accept this offer and go ahead with the transplantation?
====================================================================
What is meant by virtual crossmatch? What are the pros and cons?
What are the pros and cons?
The pros:-
Potential Benefits-cont’d
Laboratories?
Transplant programs?
Others?
The cons:-
laboratories?
transplant programs?
others?
====================================================================
Reference
What information do you need to know to support your decision?
Will you accept this offer and go ahead with the transplantation?
yes, after an MDT discussion we will accept as a good candidate with zero cross match and no DSA.
What is meant by virtual crossmatch? What are the pros and cons?
virtual cross match is a rapid computerized cross-match among the pools of donors to identifying a high risk or sensitized recipients
PROS:
allow you a short time to access the kidney and shorten waiting time
CONS:
lesser reliable test in compared to some other types of cross-match studies
I like your decision-making in interpreting crossmatching.
Thanks a lot sir
This is a good donor with 000 mismatch and no DSAs
The important information required here is:
Would you accept to this donor?
Yes I would accept this donor and proceed with the transplant
Virtual crossmatch:
The virtual crossmatch refers to a process where the actual results of the recipient HLA Ab are compared to the donor HLA Ag to determine what the actual crossmatch results would be
The virtual crossmatch has a positive predictive value of > 85% but a low negative predictive value of 50% . This is because of the incomplete profile of the recipients HLA Ab
I like your decision-making.
Thank you Professor Sharma
What information do you need to know to support your decision?We still need to know donor and recipient blood group. The other question should aim to go through the donor’s medical history, in particular history of infections or malignancy. Recipient history of sensitization events should be taken in consideration including blood transfusion, pregnancy, previous transplantation.
Will you accept this offer and go ahead with the transplantation?Yes I will accept the kidney offer after making sure that blood group is compatible and no risk of infection transmission.
What is meant by virtual crossmatch? What are the pros and cons?The need for a final “physical” crossmatch has been significantly reduced thanks to the “virtual” crossmatch, which matches the patient’s antibody profile to the donor’s HLA type. It is mostly utilized in kidney transplants from deceased donors.
Cons
Any source of sensitization, including pregnancy, blood transfusions, and previous transplants might impact virtual crossmatch.
Pros
It matches FCM cross match
Define inappropriate antigens to reject donors.
Dear Dr Habli, a donor organ offer would be made ONLY after matching for compatibility of blood groups before HLA matching.
What information do you need to know to support your decision?
-ABO blood grouping
-HLA typing for HLA A ,B ,DR
It will be needed in this deceased donor to save time and reduce cold ischemia time
-HLA crossmatching(VXC) requiring HLA typing and solid phase screening
-DSA recent test
-CPRA
-Virological screening
-History of sensitisation need to be excluded as blood transfusion ,pregnancies as well as ,previous infections ,malignancies ,DBD or DCD
Will you accept this offer and go ahead with the transplantation?
Yes, since there is 000 mismatch and no DSA ,therefore seems to be of standard immunological risk transplant.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual cross match uses donor HLA typing and solid phase antibody screening in vitro to crossmatch results by mixing the recipient’s serum harbouring specific Ab with donor HLA antigens .
Pros
It can shorten waiting times and improve sensitised transplants outcomes .It can be carried out at the time of donor identification because of the presence of progressively sensitive and specific flow cytometry technology enabling consideration of potentially positive crossmatch which is a risk factor for donor selection therefore saving grafts.
Cons
Old serum sample with specific antibodies are used rendering crossmatch prediction not precise enough also other factors can affect the antibody specificities therefore a recent serum sample must be available within less than 3 -6 months time range.
False positive results can occur with very low Ab titre and/or non-complement binding antibodies
False negative results because all potential HLA donor antigens are classed differently and are not correctly represented
It does not identify the HLA “Null” alleles which have lower risk in SOT but can affect future transplants.
Reference
-Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017 December 24; 7(6): 276-363
Let us appreciate the importance (rather lack of it) of null alleles in solid organ transplant versus in stem cell transplant.
What information do you need to know to support your decision?
Ø Blood group for donor and recipient
Ø Cross match
Ø DSA
Ø Virology screen HBV,HCV,HIV and CMV
Ø Regarding the recipient we need to know any history of previous abortion ,miss carriage previous transplant and recent blood transfusion .
History diabetes or hypertension .
Will you accept this offer and go ahead with the transplantation?
Ø Yes. zero mismatch ,no DSA
What is meant by virtual cross match? What are the pros and cons?
Ø Virtual cross match: VXM
It is test assess immunologic compatibility between recipient and donor by analyzing result of 2 independently done physical laboratory tests –patient anti HLA antibody and donor HLA typing .
Advantage
1 increased sensitivity
2-improves risk assessment for rejection
3- improves transplantation access for highly sensitized patient
4- may be performed with stored sera there for shortening cold ischemia time .
Disadvantage :
1- Required more coordination between immunology lab personal and transplant team
2- Beads may lead to false positive result
References :
hand book of kidney transplant .
I like your decision-making.
You need not to type the whole sentence in bold or capitals. That amounts to ‘shouting.’
Thank you .. prof
What information do you need to know to support your decision?
– ABO compatibility.
– HLA compatibility
– Virology screening CMV, EBV, HIV.
– History of any sensitizing events for both donor and recipient.
– Recent cPRA
– Recent updated anti-HLA antibodies profile for the recipient.
– Virtual cross matching.
Will you accept this offer and go ahead with the transplantation?
Providing the absence of new sensitizing event and virtual cross match was negative. Yes, this donor can be accepted as is a good match and no DSA.
What is meant by virtual crossmatch? What are the pros and cons?
– VXM is a risk assessment tool, determine the immunologic compatibility between a recipient and a donor by analyzing and comparing the results of 2 independently done laboratory tests—patient anti-HLA antibody and donor HLA typing.
-A virtual crossmatch can predict actual crossmatch results based on antibody specificity and strength detected by solid-phase assays.
-Accurate prediction relies heavily on up-to-date HLA antibody testing of recipients and complete HLA typing of donors.
Pros:
– Significantly improved organ allocation efficiency.
– Define unacceptable antigens
– Reduced testing costs.
– Shorter wait times and cold ischemia time
– VXM is potentially more sensitive than PXM to detect the presence of DSA.
– Does not require a viable cell.
– Enables transplant surgeons to examine donor organs that would not otherwise be accessible using a prospective crossmatch technique, making a possibly positive crossmatch a risk factor for donor selection.
Cons:
– The use of antibody specificity from historical sample (earlier than 6 months) could not predict a crossmatch with certainty.
– False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies or denatured human leukocyte antigen on SAB.
– The result varies according to the laboratory’s MFI cutoff values
– False negative results due to:
– The fact that the list of all potential HLA donor antigen, cannot be correctly represented.
– HLA structure present on the SAB assays differs between the 2 vendors that are currently available
– Shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen
– Inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect).
– VXM does not identify the HLA “Null” alleles. Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
References:
-Human leukocyte antigen typing and crossmatch: A comprehensive review Mohammed Mahdi Althaf, Mohsen El Kossi, Jon Kim Jin, Ajay Sharma, Ahmed Mostafa Halawa World J Transplant 2017 December 24; 7(6): 276-363
-Principles of Virtual Crossmatch Testing for Kidney Transplantation Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani Muthukumar Kidney Int Rep (2022) 7, 1179–1188
Let us appreciate the importance (rather lack of it) of null alleles in solid organ transplant versus in stem cell transplant.
What information do you need to know to support your decision?
· ABO compatibility
· HLA matching (here 000 mismatch)
· Donor condition: infection, malignancy, DCD or DBD, and others
· Recent DSA
· History of sensitization (blood transfusion, abortion, and previous transplant)
Will you accept this offer and go ahead with the transplantation?
Yes, I will accept in case of this best HLA match, no DSA, and –ve virtual crossmatch
What is meant by virtual crossmatch? What are the pros and cons
*The ELISA, flow cytometry or Luminex assay is run against a fixed panel of HLA antigens from past organ donors in a large computerized database and the percentage of specific unsuitable antigens reported
*This “virtual cross-match” is called as calculated PRA (cPRA) in the US and calculated Reaction Frequency (cRF) in UK
*PRA/cPRA measures the level of HLA sensitization, the recipients’ likelihood of a positive
cross-match but cannot determine the presence of antibodies against a certain donor kidney
Pros:
1. Quick (shorter wait times)
2. Tests against a large number of fixed and consistent HLA antigens
3. Can be performed at the time of donor identification
4. Consider a potentially positive crossmatch depending on a risk factor for donor selection
Cons:
1. The use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty
2. False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies
3. False negative results due to the fact that the list of all potential HLA donor antigens have been classed differently
4. The results from are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well
5. Does not identify the HLA “Null” alleles (are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface)
References
1. Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant. 2017 Dec 24;7(6):339-348. doi: 10.5500/wjt.v7.i6.339. PMID: 29312863; PMCID: PMC5743871.
2. Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi: 10.1016/j.ekir.2022.03.006. PMID: 35685330; PMCID: PMC9171621.
3. Mohanka R, E Kosi M, Jin J, Sharma A, Halawa A. Careful Interpretation of HLA Typing and Cross-Match Tests in Kidney
Transplant. JOJ uro & nephron. 2017; 3(5): 555625. DOI:
Let us appreciate the importance (rather lack of it) of null alleles in solid organ transplant versus in stem cell transplant.
What information do you need to know to support your decision?
Will you accept this offer and go ahead with the transplantation?
What is meant by virtual crossmatch? What are the pros and cons?
Thankyou but you need to revise some facts:
the antigens are on the lymphocytes so what you need from the donor (deceased) is a lymph node or a punch from the spleen but not kidney.
VXM is between donor ANTIGENS and recipient DSAs ( antibodies)
Other needed information
1- History : Patient gender and ethenicity ,presence of any chronic medical illness as diabetes or HPN or any infectious diseases specially HIV . HBV and HCV or malignancy.
2- Cause of death, utilization of positive inotropes , UOP ,presence of end organ damage , his last lab including KFT
3- ABO and results of virtual cross match
Will you accept this donor
Yes, I will accept his if no absolute contraindication was found as no active malignanacy or infection . From immunological point of view this is a suitable donor as 000 mismatch and no DSA .
Virtual cross match
Used to assess immunological compatibility between donor and recipient and to detect the presence of preformed DSA through comparing the results of tissue typing of both donor and recipient that were perfomed separarely .It’s virtual as it doesn’t include actual physical tissue examination and it helps to shorten cold ischemia time ,but it does not predict the results of physical cross match , so it is better to preserve VXM for low risk ,non sensitized patient .
Pros of VXM:
1- Shorten cold ischemia time .
2- Comparable results with physical cross match specially in non sensitized recipients
3- Lower cost and better results in detecting both serological and epitop DSA
Cons of VXM:
1- Some alleles are missed in LSAB kits as LSAB contains only 100 allele for each HLA class , so require specific kits to test for these alleles .
2- False results may occur from denatured protients on LSAB beads.
3- Cannot detect presence or effect of inhibitory mediators in recipient serum .
4- Requires coordination between labs as there is variation in SAB beads according to manufacrurer
Ref:
1- Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188. doi
2- Peng B, Zhuang Q, Yu M, Li J, Liu Y, Zhu L, Ming Y. Comparison of Physical Crossmatch and Virtual Crossmatch to Identify Preexisting Donor-Specific Human Leukocyte Antigen (HLA) Antibodies and Outcome Following Kidney Transplantation. Med Sci Monit. 2019 Feb 3;25:952-961
Thank you so the important prerequisites are a recent within 3-6 months DSA.
history of sensitising event which you mentioned.
1) What information do you need to know to support your decision?
Blood grouping, history of sensitization (pregnancies, previous transplants and blood transfusions).
2)Will you accept this offer and go ahead with the transplantation?
Yes. I will accept this donor with 0,0,0 HLA mismatch, which is good and negative DSA because renal transplantation remains the best option for patients with (ESRD) than dialysis.
3) What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatching (VXM):
In (VXM), both donor HLA typing and solid phase antibody screening are employ together.
It is not absolutely a crossmatch in the sense of mixing serum and lymphocytes.
The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
It is helps in cases when a prospective crossmatch strategy not available, and thereby, allows to consider a potentially positive crossmatch a risk factor for donor selection
Titres, specificities, and presence or absence of antibodies could significantly vary over time. Thus, the use of antibody specificity from historical serum sample (earlier than six months) could not predict a crossmatch with certainty. Other factors that can influence antibody specificities should be considered, and these include pregnancies, transplants and blood transfusions.
The VXM should, therefore, be done considering all available serum results including at least one recent within less than 3-6 mo for a given patient. False positive results of VXM may arise where there are significantly low titre and/or non-complement binding antibodies, thereby, resulting in the wrong exclusion of potential donors. The VXM can also give false negative results due to the fact that the list of all potential HLA donor antigens have been classed differently and, therefore, can not be correctly represented. The results from VXM are not a hundred percent accurate and current practice mandates an actual crossmatch be performed as well. Furthermore, VXM does not identify the HLA “Null” alleles. Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. In excess of 190 null alleles have been identified across HLA class I and II. There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation. A recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product and, therefore, transplanted with a donor bearing the expressed antigen. This mismatch is not life threatening but can affect future transplantation. In contrast, where a donor null allele is misidentified as a fully expressed product and subsequently transplanted into a recipient bearing the expressed antigen results in no humoral rejection and is well tolerated.
Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017; 7(6): 339-348 [PMID: 29312863 DOI: 10.5500/wjt.v7.i6.339]
Well done.
Dear All
Thank you for your reply
I agree with the virtual crossmatch, but what criteria are required to perform a VXM in the index case?
What is “HLA null allele” meant and how would they affect the results of VXM?
You have missed an essential requirement that is needed to perform a VXM.
Please read one of my publications: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5743871/
What criteria are required to perform a VXM in the index case?
Rapid crossmatching in sensitized recipients, from a cadaveric Donor, shown to improve outcomes in sensitized recipient.
Identify best donor in short time.
What is “HLA null allele” meant and how would they affect the results of VXM?
Null HLA alleles have identifiable DNA sequences with molecular typing, but do not express HLA products on the cell surface. Thus; the recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product, which may result in no no humeral rejection that is tolerable.
I note your reply. I agree that VXM is for cadaveric transplant work-up.
thank you Prof. Ajay
Thank you Dr Hassan for the HLA null allele but
Have you read the question carefully about what criteria are required to perform a VXM in the index case?
When using VXM, we rely on donor HLA typing, so if null allele is misidentified as fully expressed antigen, this may change the decision due to finding of DSA in the recipient, that would be not significant
HLA alleles that have identifiable DNA sequences with molecular typing but with no cell surface antigen expression. These alleles termed “null” HLA alleles are of less immunological significance
VXM offers shorter waiting time, better with deceased donation, provide more donors who were not accepted before by conventional CM, so it can be better in highly sensitized patient
I note your reply. I would add that VXM is for cadaveric transplant work-up.
Do you think null” HLA alleles ‘are of less immunological significance’?
Are you aware that your VXM result will be reliant on donor antigens which are actually ‘in real life’ are not expressed on the donor cell surface, they are only detected on the level of DNA sequencing?
yes it is less immunological significance
Let me ask the question in another way? Could the null HLA alleles cause false positive VXM?
no, it may leads to false negative as it is unidentified by VXM as it has no HLA expression on cell surface
Thank you prof,
I note the importance (rather lack of it in solid organ transplant) of null alleles in solid organ transplant versus in stem cell transplant.
Yes, thank you prof
Thank you Dr Lomatayo
You referred to ‘Identification of the donor, solid phase antibody screening, donor typing’ as essential requirement that is needed to perform a VXM?
Do you think these are the essential requirement to perform VXM?
Most welcome prof, Moshen
Thank you. Does it matter when these tests done?
old versus recent and what could be considered reasonable time for these tests
Welcome prof.
1.< 30 days for sensitized patients
2.> 30 days for unsensitized patient
– Donor HLA typing and solid phase antibody screening are needed to perform VXM
-Null HLA alleles are HLA alleles with identifiable DNA sequences with molecular
typing but with no cell surface antigen expression. The null HLA alleles are of less immunological significance
Let us appreciate the importance (rather lack of it) of null alleles in solid organ transplant versus in stem cell transplant.
Thank you Dr Doaa
What about solid phase antibody result was available for this recipient a year ago? Do you think this would be appropriate for VXM.
I think a recent one is needed
Many thanks Prof.Halawa
What is “HLA null allele” meant and how would they affect the results of VXM?
Luis Alberto Marin Rubio, Jose Daniel Aroca‐Aguilar, Mar Luis‐Hidalgo, Julio Escribano, Jesus Ontañon, RNA and protein expression analysis of allele: A null allele renamed as , HLA, 10.1111/tan.14537, 99, 3, (160-166), (2022)
====================================================================
I agree with the virtual crossmatch, but what criteria are required to perform a VXM in the index case?
Virtual crossmatch (VXM) combines donor HLA typing and solid phase antibody screening to forecast in vitro crossmatch results, leading to shorter wait times and improved outcomes for sensitised transplant recipients.
Yes, co-ordination between lab and clinicians is the key to discuss potential false + and false -.
What is “HLA null allele” meant and how would they affect the results of VXM?
You have missed an essential requirement that is needed to perform a VXM.
Excellent answer, well done. I could not add any comments.
Thanks a lot.
“null” HLA alleles :
The ability to differentiate HLA alleles that have identifiable DNA sequences with molecular typing but with no cell surface antigen expression. These alleles termed “null” HLA alleles are of less immunological significance
Criteria are required to perform VXM:
· To assess alloantibody
· For patient with no identified alloantibody
· Recipient with history of blood transfusion ,previous transplant ,pregnancy (female ).
We do VXM for cadaveric renal transplant, Donor HLA typing and recent recipient SAB are required.
Null HLA alleles has no cell surface antigen expression ir serologically detectable produces although there is identifiable DNA sequences with molecular
typing. There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation but this risk is lower in solid organ transplantation. The risk occur mostly when the recipient null allele is misidentified as fully expressed product as this will lead to the development of DSA in the recipient against that antigen after transplantation which is still not life threating but can affect future transplant.
Dear All
what criteria are required to perform a VXM in the index
case?
VXM is required in deceased kidney donors for rapid matching
and shorter cold ischemia time .
To perform VXM both donor HLA typing and solid phase antibody screening are utilised together.
Titres, specificities, and presence or absence of antibodies could significantly vary over time so the results must be recent within 3 months
taking into consideration recent sensitization events .
What is “HLA null allele” meant and how would they affect
the results of VXM?
Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
In excess of 190 null alleles have been identified across HLA class I and II.
There is a significant risk where a null allele is
misidentified for its fully expressed counterpart in stem cell transplantation.
However, the risk is slightly lower in solid organ transplantation.
A recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product
and, therefore, transplanted with a donor bearing the expressed antigen.
This mismatch is not
life threatening but can affect future transplantation.
The risk of missing null allele is high in VXM, as donor HLA typing may not detect this null allele due to lack of cell surface product, and its not expressed as antigen.
And we can’t determine the donor’s DSA against this allele which will affect the graft if present
what criteria are required to perform a VXM in the index case?
A VXM is a tool to reduce cold ischemia time in cadaveric transplantation
To perform a VXM, 2 things are essential:
1) HLA typing of the donor
2) Solid phase assay/ Single antigen bead (Luminex) test of the recipient to detect anti-HLA antibodies in the recipient. The test should be as recent as possible (not more than 3 months old), and a sensitizing event like blood transfusion/ pregnancy etc should not have occurred after the last single antigen bead test.
What is “HLA null allele” meant and how would they affect the results of VXM?
A VXM does not identify ‘null alleles’, which have DNA sequences identifiable on molecular typing but do not express HLA on cell surface. In such a scenario, donor null allele can be identified as a fully expressed product by the recipient, and DSA can develop in the recipient if the expressed antigen is not present in the recipient, leading to difficulties in future transplantation. It will have no effect if the recipient expresses the antigen.
Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. In excess of 190 null alleles have been identified across HLA class I and II.
There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation.
For a virtual crossmatch to be allowed the results for the recipient need to be less than six months old. Factors like pregnancy and blood transfusion need to be taken into account as well
One of the key requirements of a virtual crossmatch is that a physical crossmatch has to take place which in this case will not be possible.
The virtual crossmatch also does not take into account the null alleles
HLA null alleles refers to the genetic mutations that code for non-functional proteins or proteins that are not expressed on the cell surface. Null alleles produce no serologically identifiable products. These can cause problems in transplantation especially for HSCT and less so for SOT
-The use of VXM can lead to shorter wait times and improved outcomes for sensitised transplant recipients.
-This is particularly important in deceased donor renal transplantation. Quick results mean less cold ischemia times.
-Null HLA alleles; are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface.
-In excess of 190 null alleles have been identified across HLA class I and II.
-There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation.
Not slightly, but much lower
HLA null alle DNA sequence with molecular typing but no cell surface antigen expression and less immunogenic significance.
VXM is need donor HLA typing and recipient solid phase assay
the risk of null alleles is misleading for its fully expressed in stem transplantation, however, the risk is lower in solid organ transplantation which leads to DSA formation but has no life threaten effect.
References
Patel R, Terasaki PI. Significance of the positive crossmatch test in kidney transplantation. N Engl J Med. 1969;280(14):735–739. [PubMed] [Google Scholar]
Risk is much lower in solid organ transplant
What criteria are required to perform a VXM in the index case?
The VXM involves matching of HLA typing of the donor and the presence of antibodies in the recipient serum, which is done by using a solid phase assay on a historical serum of the patient .There is no physical mixing of recipient serum with the donor lymphocytes.
V XM more sensitive than Actual XM
To perform a VXM we need:
1) HLA typing of the donor
2) SAB (Luminex) test to detect anti-HLA antibodies in the recipient, For last three month and a sensitizing event like blood transfusion/ pregnancy etc should not have occurred after the last recent single antigen bead test.
What is “HLA null allele” meant and how would they affect the results of VXM?
HLA null allele DNA sequence with molecular typing but no cell surface antigen expression and less immunogenic significance. VXM is need donor HLA typing and recipient solid phase assay the risk of null alleles is misleading for its fully expressed in stem transplantation, however, the risk is lower in solid organ transplantation which leads to DSA formation but has no life threaten effect.
-Not all alleles represented on beads (too many )
-Not all proteins currently type for use historical serum => patient have entire immune history before listing cannot predict what you have never tested and cannot assess for potential immune memory
Yes, that is very sensible
The requirement to perform VXM
VXM method helps to shorten waiting time and could lead to an improved outcome in the sensitized recipient.
HLA null allele
These are alleles that have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. They are of less immunological significance and can not be detected by VXM.
Yes, that is right
The virtual crossmatch requirements:
· the VXM does not require viable donor cells but rather relies on complete HLA typing of the donor and current antibody assessment of the recipient.
· The prerequisite to benefit from the advantages of just VXM testing is the determination of unacceptable antigens by SAB assay and to predict the actual PXM results.
The null HLA:
· HLA null alleles: code HLA antigens with low or no cell surface expression.
· Null alleles are not detectable by standard serological typing methods and may be overlooked/or incorrectly assigned by available DNA methods.
· The failure to identify an HLA null allele as a non-expressed variant in the stem cell transplantation setting may result in an HLA mismatch that is highly likely to stimulate allogeneic T cells and to trigger graft-vs-host disease.
· The prevalence of HLA null alleles may be around 0.3% or even higher(1).
· For some HLA null alleles, the translation into a truncated polypeptide chain seems possible, which thus might act as minor histocompatibility antigens.
· Complete sequence of exons 2 and 3 for class I and exon 2 for class II molecules by sequencing-based typing was deemed the best technique in reducing problems with ambiguities and null alleles(1)
References
1. Elsner HA, Blasczyk R. Immunogenetics of HLA null alleles: implications for blood stem cell transplantation. Tissue Antigens. 2004 Dec;64(6):687-95. doi: 10.1111/j.1399-0039.2004.00322.x. Erratum in: Tissue Antigens. 2006 Aug;68(2):191. PMID: 15546342.
2. Oudshoorn M, Horn PA, Tilanus M, Yu N.Typing of potential and selected donors for transplant: methodology and resolution Tissue Antigens. 2007 Apr;69 Suppl 1:10-2. doi: 10.1111/j.1399-0039.2006.758_5.x.PMID: 17445154
Yes, it might occasionally pose as minor histocompatibility
-The donor HLA typing and solid phase antibody screening are used simultaneously.
-HLA null alleles despite not expressing HLA products on the surface have similar DNA sequencing on molecular typing and thus may either show a false positive in some instances from the list of donor HLA donor antigens classed differently and misinterpreted or low titers of complement binding antibodies on the other hand may lead to false positives.
what criteria are required to perform a VXM in the index case?
Consider a virtual crossmatch when there are sufficient data on a patient’s alloantibody status to meet the transplant program- specific criteria. Also require donor typing to include HLA & other histocompatibility antigens to which antibodies have been identified in the recipient.
Requirement to perform VXM:
1. the donor HLA typing result.
2. the result of the recipient’s solid-phase antibody screening.
VXM method helps to shorten waiting time and could lead to an improved outcome in the sensitized recipient.
HLA null allele:
These are alleles that have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. They are of less immunological significance and can not be detected by VXM.
Null HLA alleles are ones have identifiable DNA sequences with molecular typing but do not express HLA products on the cell surface. In excess of 190 null alleles have been identified across HLA class I and II.
There is a significant risk where a null allele is misidentified for its fully expressed counterpart in stem cell transplantation. However, the risk is slightly lower in solid organ transplantation.
A recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product and, therefore, transplanted with a donor bearing the expressed antigen. This mismatch is not life threatening but can affect future transplantation.
In contrast, where a donor null allele is misidentified as a fully expressed product and subsequently transplanted into a recipient bearing the expressed antigen results in no humoral rejection and is well tolerated.
Ischemia time.
Prolonged cold ischemic time certainly has an adverse effect on the function of all
transplanted organ.
Autopsy report of the cadaveric donor.
Determine whether an autopsy was not performed due to a perceived risk of
transmission of a communicable disease.
If an autopsy was performed, whether any special precautions were taken that would
suggest there was special concern over the risk of transmission of a communicable
disease from the donor.
The donor medical history interview is a documented dialogue concerning the donor’s
medical history and relevant social behavior.
Physical signs of a relevant communicable disease and for signs suggest
Communicable disease and for signs suggestive of any risk factor for such a disease. (1)
Yes after VXM.
Advise patient of communicable disease risk.
Based upon a physician’s request documented.
The VXM test uses the results of 2 independently done physical laboratory tests and
does not involve mixing of serum and cells. Instead, immune compatibility is assessed
by analyzing results of donor HLA typing and patient antibodies against HLA.(2)
What are the potential benefits of virtual crossmatches for patients?
Less time needed for evaluation of compatibility (particularly with thoracic transplant
patients); results in more efficient use of the system
Ø Reduced cold ischemia time .
Facilitates matching over larger geographic area, renal paired donations, and the
transplantation of more highly sensitized patients.
Ø Can result in improved access for sensitized patients.
Ø Increased sensitivity and specificity of testing can lead to a better matched
donor/recipient .
Ø More specific than serologic crossmatches-(includes patient history).
Ø Less likely to deny access for a false positive physical crossmatch.
Ø Reduced cost (3)
Ø Does not preclude the performance of a physical XM; however, this may be
completed concurrent with or after transplantation .
Ø Aids in risk assessment for patient desensitization needs.
For Laboratories:
– Increased efficiency, which allows for more focus on patients with problems and results
in cost savings.
Ø Decreased on-call time expenditure by testing personnel.
Ø Allows for better coordination and communication with transplant programs.
Ø Improved quality management with better patient and transplant program satisfaction.
For Transplant programs:
Ø Reduced ischemia time .
Ø Improved access to transplantation for immunologically and geographically .
disadvantaged candidates, which results in improved transplant physician and patient
satisfaction.
Ø Fewer unexpectedly positive physical crossmatches leads to more efficient use of
transplant personnel .
Ø Improved risk assessment for rejection .
Ø Allows for optimized immunosuppression and desensitization protocols.
Ø Flexibility in managing transplant related logistics (i.e. OR schedules) .
Ø Cost savings others?
Ø Benefits donor families in that there is a greater possibility that donated organs will be
used .
Ø Cost savings to payers.
What are the potential disadvantages of virtual crossmatches to:
To patients?
Ø Based on the program’s criteria for crossmatches, there is potential to deny use of a
donor organ that could be successfully transplanted.
Ø Requires patient to receive and understand more complicated information.
Ø Negative crossmatch (physical or virtual) does not guarantee compatibility.
To Laboratories?
Ø Potentially more difficult for staff to maintain competency in performing physical
crossmatches when they are done less frequently .
Ø Increased unreimbursed interpretation time.
Ø Requires more coordination with transplant program.
To Transplant programs?
Ø Program staff have to learn a new interpretive vocabulary .
Ø Additional time and work to ensure that patients understand their risk and get all the
information on time.
References:
1- Eligibility Determination for Donors of Human Cells, Tissues, and Cellular and Tissue-
Based Products (HCT/Ps). U.S. Department of Health and Human Services Food and
Drug Administration Center for Biologics Evaluation and Research August 2007.
2-Madu C. Bhaskaran et al. Principal of virtual Cross matching testing for Kidney
Transplantation. Ki report; volume 7.issue 6, P1179-1188, June2022.
Thank you for your reply
I agree with the virtual crossmatch, but what are the criteria required to perform a VXM in the index case?
You have missed an important and essential requirement that is needed to perform a VXM.
No tissue available for further final cross matches.
short time for the operation ,need to reduce ischemia time.
1- ABO should be known
2- yes will accept based on ABO and no DSA and 000 mismatch
3-virtual cross match is to compare HLA typing of the patient with donor, and consider antiHLA antibodies to the donor in the recipient, without doing wet cross match between the serum of the patient and lymphocyte of the donor
pros it is web based program , time saving, can be used in highly sensitized patient without paying attention to cPRA , can predict physical cross match and can replace it
the process is easy after introduction and usage of SAB technique, it is accurate and faster than physical CM, it can sort the patients depends on HLA matching, and CPRA.
cons still has time to review HLA of the patient and donor and detect unacceptable genes
N. Jamshidian Tehrani,B. Geramizadeh, S. A. Malekhosseini,S. Nikeghbalian, A. Bahador, S. Gholami, G. A. Raees Jalali, J. Roozbeh, M. H. Anbardar, N. Soleimani, N. Rasaei, S. Mohammadzadeh. Virtual Crossmatching in Kidney Transplantation, Shiraz Experience in Development of a Web-Based Program. Int J Organ Transplant Med. 2021; 12(2): 20–25.
You mean unacceptable ANTIGENS.
Please elaborate more on Cons.
Thank you for your reply
I agree with the virtual crossmatch, but what are the criteria required to perform a VXM in the index case?
You have missed an important and essential requirement that is needed to perform a VXM.
What information do you need to know to support your decision?
1. Check the proposed donor medical file, history of infections, medications, alcohol and sexual history, cardiac history, history of blood transfusion.. etc.
2. ABO compatibility, and cross match – lymphocytotoxicty, c-PRA , and DSA.
3. Type of donor death is it cardiac, or brain death, as DBD has better graft survival as well as less risk for delayed graft function.
4. CMV, EBV, and other viral screening for both donor and recipient.
5. The recipient cardiac status, screening for breath and cervical cancers, primary disease, smoking history.
Will you accept this offer and go ahead with the transplantation?
Yes; I’ll accept this kidney for transplantation, however the is 000 mismatch which gave and excellent prognosis.
What is meant by virtual crosmatch? What are the pros and cons?
Virtual crossmatch is a process assessing the result of solid phase and cell bases HLA antibody identification assays to predict, correlate to the result of physical crossmatch.
Pros: (1) Increase the likelihood of crossmatch compatible donors to highly reactive patients.
(2) leads to successful transplantation to highly sensitized HD patients.
Cons: (1) false negative allele specific antibodies/unique epitope not identified by single antigen beads [almost 20%].
(2) false positive with low levels of HLA antibodies, compromised donor cells and antibodies against denatured HLA antigens [5%].
References:
(1) UpToDate- evaluation of deceased organ donor.
(2) Morris AB, Sullivan HC, Krummey SM, Gebel HM, Bray RA. Out with the old, in with the new: Virtual versus physical crossmatching in the modern era. HLA. 2019 Dec;94(6):471-481. doi: 10.1111/tan.13693. Epub 2019 Oct 17. PMID: 31515937; PMCID: PMC7341023.
(3) Peacock S, Briggs D, Barnardo M, Battle R, Brookes P, Callaghan C, Clark B, Collins C, Day S, Diaz Burlinson N, Dunn P, Fernando R, Fuggle S, Harmer A, Kallon D, Keegan D, Key T, Lawson E, Lloyd S, Martin J, McCaughan J, Middleton D, Partheniou F, Poles A, Rees T, Sage D, Santos-Nunez E, Shaw O, Willicombe M, Worthington J. BSHI/BTS guidance on crossmatching before deceased donor kidney transplantation. Int J Immunogenet. 2022 Feb;49(1):22-29. doi: 10.1111/iji.12558. Epub 2021 Sep 23. PMID: 34555264; PMCID: PMC9292213.
You mean in your first two (PROS) is that it will help you choose a more suitable donor.!
Thank you for your reply
I agree with the virtual crossmatch, but what are the criteria required to perform a VXM in the index case?
You have missed an important and essential requirement that is needed to perform a VXM.
What criteria are required to perform a VXM in the index case?
Rapid crossmatching in sensitized recipients, from a cadaveric Donor, shown to improve outcomes in sensitized recipient.
Identify best donor in short time.
What is “HLA null allele” meant and how would they affect the results of VXM?
Null HLA alleles have identifiable DNA sequences with molecular typing, but do not express HLA products on the cell surface. Thus; the recipient will have the risk of developing DSA for the mismatch where the null allele is misidentified as a fully expressed product, which may result in no no humeral rejection that is tolerable.
yes; in a short time period -as from cadeveric one.
Information needed to support my decision
Donor and Recipient blood group should be known ,also cPRA and the sensitization of the patient like Blood transfusion ,vaccination history or history of transplantation should be known along with Viral serology of the donor and virtual cross match result. Cause of death in a road traffic accident-whether the patient was DCD OR DBD as it has impact on graft survival.
Will you accept this offer and go ahead with the transplantation
Offer can be accepted but only after knowing the ABO compatibility and taking detailed history of the donor and ruling out infections in the donor and if no other option available.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual cross match is usually carried out for deceased donor transplants.In virtual cross match, anti-HLA antibodies detected by Luminex method are matched to HLA typing report of donor without doing the actual cross match.
PROS:
It has resulted in improved organ allocation and
Less waiting times for transplantation.
HLA typing of donor is required just without the need of donor cells.
cold ischemia time is less and easily excludes unacceptable antigens.
CONS:
False positive result may occur because of denatured HLA antigen on bead, low titer and/or non-complement binding antibodies.
SAB by luminex for recipient may need to be repeated every three months due to change in antibodies because of sensitization like pregnancy ,vaccination,infection, blood transfusion,and previous transplantation.
Lot of coordination between Immunology Lab personal and transplant team.
Cutoff values of MFI , thus, are different among laboratories not standardized.
References:
1-Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017; 7(6): 339-348
2- Bhaskaran MC, Heidt S, Muthukumar T. Principles of Virtual Crossmatch Testing for Kidney Transplantation. Kidney Int Rep. 2022 Mar 15;7(6):1179-1188
Well done.
-What information do you need to know to support your decision?
-Will you accept this offer and go ahead with the transplantation?
-What is meant by virtual cross-match? What are the pros and cons?
Virtual cross-match;
Pros:
Cons:
Source;
Well done.
Sensitization history
Virology of donor and recipient
ABO typing
High resolution DNA-based HLA typing and the solid-phase assays
CPRA
Yes, after risk stratification at the recipient center for kidney transplantation.
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests—patient anti-HLA antibody and donor HLA typing. The American Society for Histocompatibility and Immunogenetics defines VXM test as an assessment of immunologic compatibility based on patient’s alloantibody profile compared with donor’s histocompatibility antigens. (1)
In contrast Physical crossmatch (PXM) tests, such as complement-dependent cytotoxicity crossmatch (CDCXM) and flow cytometry crossmatch (FCXM), require mixing of patient serum and donor cells, are labor intensive, and are logistically challenging
The goal of VXM is pretransplant risk stratification the output of VXM could be reported as a dichotomous positive or negative or as a probability value and has not been standardized.
Advantages
Increased sensitivity
May be performed with stored sera therefore shortening cold ischaemia time
Improves transplantation access for highly sensitized patients
Improves risk assessment for rejection
Disadvantages
1- Denatured human leucocyte antigens on single antigen beads may lead to a false positive result
2- Requires more coordination between immunology lab personnel and transplant team
A false negative virtual crossmatch can arise for a number of reasons.
– Incomplete typing of the donor,
– As well as donor specifc antibodies in the recipient serum against a unique HLA epitope which is not available on the SAB panel (2)
False positives may also occur as a result of
– Antibodies directed at HLA epitopes that come about secondary to denatured HLA antigens on the SAB (3)
– Due to presence of null alleles, which are not expressed as antigens on the cell surface in vivo (4)
Conclusion
Implementation of VXM-based approach has resulted in statistically significant reduction in cold ischemia time without an increase in hyperacute rejection episodes. Though there are considerable challenges, VXM is expected to be used more often in the future, depending on the transplant center’s tolerance of immunologic risk.
Ref
Well done .It will be clearer to mention :
Causes false negative SAB
Causes of false positive SAB.
What information do you need to know to support your decision?
Will you accept this offer and go ahead with the transplantation?
What is meant by virtual crossmatch? What are the pros and cons?
Advantages
Disadvantages
References
1.2009 Annual Report of the U.S. Organ Procurement and Transplantation Network and the Scientific Registry of Transplant Recipients: Transplant Data 1999-2008. U.S. Department of Health and Human Services, Health Resources and Services Administration, Healthcare Systems Bureau, Division of Transplantation, Rockville, MD.
2.Beaupré RA, Morgan JA. Donation After Cardiac Death: A Necessary Expansion for Heart Transplantation. Semin Thorac Cardiovasc Surg 2019; 31:721.
3.Sánchez-Fructuoso AI, Marques M, Prats D, et al. Victims of cardiac arrest occurring outside the hospital: a source of transplantable kidneys. Ann Intern Med 2006; 145:157.
Well done.
What information do you need to know to support your decision?
Sensitization history since the last screening is required (pregnancy, blood transfusion, abortion) of both the potential donor and recipient.
Vaccination schedules and recent infections must be considered.
When was the last screening of the potential donor?
Will you accept this offer and go ahead with the transplantation?
Yes, the absence of HLA and ABO mismatches added to the absence of antibodies against the donor makes the organ compatible and without the need for severe immunosuppression.
However, I would follow up more closely with DSA dosage by SAB after transplantation, as I do not have a recent crossmatch and DSA.
What is meant by virtual crossmatch? What are the pros and cons?
Virtual crossmatch (VXM) test assesses immunologic compatibility between recipient and potential donor by analyzing the results of 2 independently done physical laboratory tests, patient anti-HLA antibody and donor HLA typing
A positive T cell CDCXM result is considered an absolute contraindication for transplantation because of its association with hyperacute/accelerated rejection. A positive B cell CDCXM result or a positive FCXM result increases the risk to an intermediate level and may need desensitization therapy prior to transplant but is not considered an absolute contraindication for transplantation, although regional differences in policies exist. It will reduce cold ischemia time
A high-percentage PRA implied a high probability of a positive crossmatch result. However, because CPRA is based on unacceptable antigens, kidneys with those antigens are not offered to a patient. Thus, an actual offer for a patient with high CPRA taking the unacceptable antigens into account implies a high probability of a negative crossmatch result. Importantly, although the broadness of HLA sensitization is determined by the CPRA and influences organ allocation, in terms of immunologic risk for the recipient, it is the donor specificity, not the broadness of sensitization, that is associated with allograft outcome.
Thank you Filipe but your answer needs to be around defenition of VXM ,Its PROS and CONS.Try again.
Any history of recent sensitizing events? (blood transfusion, pregnancy or abortion).
Recent illness, infection, or vaccination.
What is the date of the latest blood sample from the potential recipient?
Yes, provided that there is no new sensitizing event and the latest sample was within 3 months.
In virtual crossmatch (VXM), the immunologic compatibility between a patient and a donor is determined in silico (In a computerized model).
For nonsensitized patients who do not have circulating antibodies, physical crossmatch(PXM) results against any prospective donor can be assumed to be negative.
Many transplant centers have reported their successful results of proceeding to transplant based on VXM results without pretransplant PXM.
Waiting for PXM increases cold ischemia time which associated with delayed graft function, organ loss, and graft failure. However, depending on VXM may have its problems also, owing to limitations of the SAB assay—in defining the absence or presence of circulating antibodies against HLA. Examples are:
1-SAB assay may not contain beads for a particular specificity.
2- SAB manufacturing issues result in lot of variability
3- HLA structure present on the SAB assays differs between the 2 vendors that are currently available.
4-Shared epitopes—antibody targets that are shared by multiple antigens on the panel tested—may result in dilution of the antibodies that bind to each antigen.
5-Inhibitory factors present in the patient serum—such as complement C1q—may interfere with antibody detection (prozone effect).
Currently, 18% of transplantations in USA is done depending on VXM.
An analysis of US registry data identified 9632 kidney transplants between 2011 and 2018 using VXM and 71,839 using PXM. Cold ischemia time was significantly lower in the VXM group (mean 15.0 hours) compared with the PXM group (mean 16.5 hours). Importantly, mortality and death-censored allograft failure were similar.
References:
1-Principles of Virtual Crossmatch Testing for Kidney Transplantation Madhu C. Bhaskaran1,2, Sebastiaan Heidt3 and Thangamani Muthukumar Kidney Int Rep (2022) 7, 1179–1188;
2-Human leukocyte antigen typing and crossmatch: A comprehensive review Mohammed Mahdi Althaf, Mohsen El Kossi, Jon Kim Jin, Ajay Sharma, Ahmed Mostafa Halawa World J Transplant 2017 December 24; 7(6): 276-363
Well done.
Information needed to support my decision
Will you accept this offer and go on with the transplant?
YES, I will accept because
What is virtual cross match
Virtual crossmatching is the method of detection of antibodies against the donor tissue by the comparison of the antiHLA antibodies of the recipient, as defined by Luminex, with the HLA of the donor. The presence of an antibodies will be reported as positive crossmatch
Pros of virtual crossmatch
Cons of virtual crossmatch
References
This a comprehensive exellent answer .
If you have a sample from this donor ( away from this index case ) when would you do a PXM as well.?
Thank prof Dawlat for the response.
I will like to do PXM within 72 hours of collecting the sample
Hematology.
1- Blood group and comprehensive metabolic profile including PT/APTT.
2- Extensive Viral serology
3- HLA of the Donor
4- cPRA of the recipient and history of Blood transfusion or transplantation
5- Depending on the above data, virtual crossmatch
Kidney can be accepted in some circumstance after complete history and available laboratory result.
Virtual cross match.
Crossmatch that involves a determination of the absence or presence of doner specific anti bodies in a patient by comparing the patients HLA antibody specificity profile to the HLA type of proposed donor without performing an actual crossmatch.
It requires.
1. Complete tissue typing of donor and recipient.
2. Anti-HLA reports of recipient by solid phase assay method.
Pros;
Gaining acceptance for an alternative approach for crossmatch
Does not require viable donor cell but totally relies on HLA typing of donor.
Virtual crossmatch is a fast procedure and can save the time for transplantation.
Reduce cold ischemia time.
Accurate virtual crossmatch also important for donor Organ can be import
Cones;
False positive results of virtual crossmatch may arise where there are significantly low titer and/or non-complement binding antibodies.
Different serum samples used for SAB versus crossmatch testing.
An Antibody identifies that is specific to an allele that donor does not have.
Nephrology and Hypertension Board Review Phuong-Chi T. Pham, MD, FASN
Out with the old, in with the new: Virtual versus physical crossmatching in the modern era
Anna B. Morris,1 H. C. Sullivan,2 Scott M. Krummey,2 Howard M. Gebel,2 and Robert A. Bray2
Well done.
1- Blood group to check the compatibility
2- blood culture and virology from the donor
3- HLA of the Donor
4- cPRA of the recipient and history of Blood transfusion or transplantation.
5- Depending on the above data, we can run the virtual crossmatch
Yes, in certain circumstances, we can accept the virtual crossmatch.
The “virtual” crossmatch, which matches the patient’s antibody profile to the donor’s HLA type, has greatly decreased the requirement for a final “physical” crossmatch. It is used mainly in cadaveric kidney transplantation.
A computerized database predicts donors with a positive crossmatch based on a candidate’s inadmissible antigens. The computer does the cross-match, as UNOS does not give kidneys from donors with projected positive cross-matches.
Pros:
1-VXM reduces wait times and improves outcomes for sensitized transplant patients.
2-VXM enables transplant surgeons to examine donor organs that would not otherwise be accessible using a prospective crossmatch technique, making a possibly positive crossmatch a risk factor for donor selection.
3- Reduction of cold ischemic time
Cons:
1: Antibody specificity from serum samples older than six months cannot predict cross-matches.
2-Low titer and non-complement binding antibodies might cause false positive VXM findings, excluding prospective donors
3-The VXM may potentially yield erroneous negative findings since all prospective HLA donor antigens have been classified differently and cannot be appropriately represented.
4-VXM does not identify the HLA “Null” alleles.
1- Handbook of Kidney transplantation
2- Althaf MM, El Kossi M, Jin JK, Sharma A, Halawa AM. Human leukocyte antigen typing and crossmatch: A comprehensive review. World J Transplant 2017; 7(6): 339-348